Intelligent electro-optical sensor array and method for analyte detection

ABSTRACT

The invention relates to a chemical sensor, sensing system and sensing method which provides for a multi-sensor, cross-reactive, sensor array having a rapid response time, dynamic modulation of sampling parameters, and real-time feedback control of sampling and detection conditions. The device and method provide for smart detection and discrimination of analytes in fluids through intelligent sampling, detection, and control algorithms. The invention further provides for a sensor array having discrete sensor elements dispersed on fluid-permeable, high surface area, porous, textured substrates. The innovative device and method exhibit high sensitivity, discrimination and detection capability for target analytes at ppb and sub ppm concentrations.

GOVERNMENT RIGHTS

[0001] The invention described herein was supported in part with U.S.Government funding under Defense Advanced Research Projects AgencyContract No. DAAK60-97-K-9502, Office of Naval Research Grant No.00014-95-1-1340, National Institutes of Health Grant No. R01-DC00228.The U.S. Government has certain rights to this invention.

FIELD OF THE INVENTION

[0002] This invention generally relates to sensors and methods fordetecting analytes. More particularly, this invention relates to opticalsensors, sensor arrays, sensing systems and sensing methods forintelligent sensing and detection of unknown materials by way ofreal-time feedback and control of sampling conditions.

BACKGROUND OF THE INVENTION

[0003] U.S. Pat. No. 4,859,864 to Smith discloses an air bubble sensorthat employs light emitting diode (LED) light sources, phototransistordetectors, and displays or alarms for detecting the presence of bubblesin a fluid sample.

[0004] U.S. Pat. No. 5,674,751 to Jaduszliwer, et al. disclose ahydrazine fuel fiber optic sensor that employs a diode laser pulsedlight source, a calorimetric fiber optic sensor system, and aphotodetector to detect changes in spectral absorption due to ppb levelsof hydrazine fuel.

[0005] U.S. Pat. No. 5,445,795 to Lancaster, et al. disclose a portableoptical sensor for detecting volatile organic compounds (VOCs) in vaporsand aqueous media. The disclosed device comprises a vapochromic sensorformed from transition metal complex salts, a sensor chamber, a vacuumpump for drawing samples into the chamber, a light source forilluminating the sensor, a light detector responsive to light reflectedfrom the vapochromic sensor, and a detection means for determining acolor change in the sensor due to the presence of VOCs. In one disclosedembodiment for fuel tank sensing, the sensor, an LED illuminating lightsource, and a photodiode detector with an optical band-pass filter areall housed within the sensor chamber and a photodiode feedback signal isprovided to a control means for adjusting a fuel metering valve viasignal processing electronic circuitry. Other embodiments employ abi-color LED that can be modulated between two wavelengths and gateddetection electronics in the detector is synchronized with LED drivercurrent to monitor small changes in reflected signals at bothwavelengths.

[0006] U.S. Patent No. 5,116,759 to Klainer, et al. discloses a vapor orliquid chemical sensor where analytes pass into a sampling cell wherethey contact sensing solutions for detection. The disclosed devicecomprises a single illumination source, an optional semi-permeableanalyte membrane, a chamber with one or more analyte-sensitive solutionscontained in a reservoir cell, a sample signal detector for detectingoptical changes in the cell due to the analyte, and an optionalreference signal detector for background signal correction. Reagent andsampling pumps are also disclosed for continuously flushing the cellwith analyte and solution reagent. The disclosed device employs diodes,lasers or lamps as an excitation source, optically responsive analytesensing solutions, detectors, and conventional electronic circuitry thatare known in the art. In a preferred embodiment, an LED is the preferredlight source and a photodiode is the preferred detector. Otherembodiments disclose a light source sensor, a source stabilizer, adetector stabilizer, and a temperature sensor and compensator circuitryfor feedback, monitoring and stabilizing the light source and detector.Disclosed embodiments include an A/D interface, alarms, display,recorders or plotters for readout, a computer and software.

[0007] Persaud and Dodd (Nature v. 299, pp. 352-355, 23 Sep. 1982)disclose an electronic nose comprised of semi-selective sensors in across-reactive sensor array designed to mimic a mammalian olfactorysystem. The disclosed sensors comprise commercially availablesemiconductor transducer gas sensors that exhibit a conductance changewhen the adsorb ambient vapors. The disclosed sensors were capable ofdetecting vapors at high concentrations ranging from 0,1 to 10 mols perliter of air. The response time for these sensors ranged from 1 to 3minutes. Measurements made with various sensor parings demonstratedselectivity toward a number of analyte vapors at high concentrations.

[0008] U.S. Pat. No. 5,512,490 to Walt and Kauer disclose a fiber opticsensor with semi-selective sensors in a cross-reactive sensor array thatemploys spectral recognition patterns for identifying and detecting avariety of analytes. The reference teaches thin film sensors formulatedby mixing polymers with dye compounds. The sensors are immobilized oneither a solid planar translucent or transparent substrate or a fiberoptic fiber or bundle. In a preferred embodiment, the substrate is atransparent optical fiber bindle in which sensors are placed on the endsof optical fibers or groups of such fibers. The sensing system taught bythis reference utilizes an arc lamp excitation source, an optical traincomprising a series of lenses, filters which are sequentially switchedto provide for changes in both excitation light wavelength and emittedlight wavelength, and a CCD camera detector which captures spatialimages of the fluorescence intensity of individual sensor elements atvarious wavelengths. The measured responses of individual sensors toanalytes are combined to form a pattern of spectral responses over timethat are unique to a specific analyte. Spectral response patterns arestored in a library and the response patterns generated from unknownsamples are compared with library patterns to identify and detect targetanalytes. Either light intensity or wavelength may be employed foranalyte determinations

[0009] U.S. Pat. No. 5,063,164 to Goldstein discloses a biomimeticsensor for detecting airborne toxins. The disclosed device comprises aporous, semi-transparent substrate which is sufficiently transmissive tolight to permit detection of transmitted light by an LED and photodiodeand is impregnated with a self-regenerating sensor. The sensor allegedlymimics the human response to toxins with regard to sensitivity andaffinity by employing a molecular encapsulant that contains a chemicalsensor reagent. The disclosed device provides for detecting a change inoptical density of the sensor which is dependent on toxin concentrationand time of exposure. For dilute analyte levels, extended exposure timesare required for adequate sensitivity and detection.

[0010] Smardzewski [Talanta 35(2):95-101(1988)] discloses amulti-element optical waveguide sensor for detecting analytes in fluidswhich comprises eight fiber optic waveguides each circumferentiallycoated with sensing material, an array of eight sequentially-activatedLEDs optically coupled to the waveguide assembly, and a single detectoror array of multiple detectors, photomultiplier tubes or photodiodes,optically coupled to the waveguide assembly. Samples are passed over theouter surface of the coated waveguides and color changes produced byanalyte interaction with the coating are monitored. In the disclosedmethod, each channel is sampled sequentially with measurements made on asingle channel before moving to a subsequent channel. In the disclosedmethod the LEDs are pulsed on and off with switching times of at leastone millisecond during measurements. The device provides for sensorsignal output to be visually displayed or input to a microprocessorpattern-recognition algorithm. CMOS analog switches/multiplexers areused in feedback loops to control automatic gain-ranging, light-leveladjustment and channel-sequencing. The detection limit and sensitivityof the disclosed device and method are limited to ppm levels.

[0011] Kopola, et al. [SPIE, Fiber Optic Sensors, v. 586, pp. 204-210(1985)] disclose an eight channel spectrophotometer for measuringspectral reflectance at discrete wavelengths. The disclosed devicecomprises eight different LED light sources that cover a wavelengthrange between 480 nm and 1500 nm, a reference and measurement photodiodedetector, a temperature controller, a fiber optic probe, signalconditioning electronics, microprocessor controller, and a display andplotter interface. In the disclosed method, measurements of both areference LED output signal and sample LED output signal, which ismodulated by the presence of an analyte, are simultaneously made with asingle LED source and each reference and measurement detectors. With thedisclosed device and method, sample measurements are time multiplexedwith measurements made sequentially for each individual LED channel.

[0012] Hauser, et al. [Meas.Sci.Technol. 6:1082-1085(1995)] disclose achemical sensor comprising LED light sources and filtered sample andreference photodiode detectors coupled to a fiber optic for detectingthe optical response of a sensing membrane to analytes. The LED ismodulated at 2 kHz. The disclosed device provides for a lightdemodulator for background signal corrections. Detector and referencesignals are ratioed to compensate for instability in the LED lightsource. The sensitivity of the disclosed device and method apparently islimited to 0.2% or 2000 ppm detection limits. Disclosed sampling timesof several minutes or more are apparently required.

[0013] Bruno, et al. [Anal. Chem. 69(3):507-513(1997)] disclose a sixchannel sensor array for detecting blood analytes. The disclosed devicecomprises LED light sources, excitation and emission filters, photodiodedetectors, pH membrane sensors and electronic circuitry. The deviceprovides for modulating LED driving current and photodiode gain factorsand providing output to a computer via an A/D/ converter for display andanalysis of data and control of fluid flow to the sensor. The disclosedsensor response time is approximately 30 seconds with a sampling timeranging from 1 to 15 minutes for each sensor. Sensitivity of the deviceis limited by signal noise caused by temperature and pressure variationsdue to sample fluid flowing through the sensor cell. An additionallimitation with the disclosed device and method is a diminishedresponsivity of sensors with extended light exposure during sampling dueto photobleaching.

[0014] Holobar, et al. [Anal.Methods and Instrum. 2(2):92-100(1995)]disclose a double-beam, flow-through pH sensor that employs a samplesolution pump, an LED light source and two filtered photodiodes, one asa reference detector and the other as a sample detector. The disclosedsensor response time is approximately 20-30 seconds.

[0015] Boisde, et al. [Chemical and Biochemical Sensing with OpticalFibers and Waveguides, Artech House (Boston, 1996)] have reviewed thestate of fiber optic chemical sensor art and have shown that LEDexcitation light sources, photodiode detectors, and multi-channel sensorwavelength multiplexing and spatial multiplexing are known in the art.

[0016] Taib, et al. [Analyst 120(6):1617-1625(1995)] have reviewedsolid-state fiber optic sensor instrumentation and have shown that LEDlight sources, fiber optic light guides, optical transducers for analytedetection, amplifiers, signal processors and output devices are allknown in the art of chemical sensor technology. The authors note thatLEDs are particularly amenable to high frequency electronic modulation,that the response time of photodiode detectors was in the microsecondrange, and that the use of multiple sensor channels with filtered LEDsand photodiodes and microprocessor control of pulsed of LED sources canprovide advantageous simultaneous multi-channel/multi-parametermeasurements. The authors additionally note that multi-channel sensorsmay be coupled to microprocessors to carry out parallel signalprocessing under software control and thereby exploit the capabilitiesof pattern recognition and artificial neural network methods.

[0017] Despite the many advantageous features provided by currentchemical sensor technology, there is a need for a chemical sensor,sensing system and sensing method which provide for a multi-sensor,cross-reactive, sensor array having a rapid response time, a rapidsampling time, dynamic modulation of sampling and detection parameters,intelligent feedback control of analyte sampling conditions, smart modesampling, smart detection through application of sophisticated analytedetection algorithms, and high sensitivity, discrimination, anddetection capability for a variety of target analytes at sub ppm to ppblevel concentrations.

SUMMARY OF THE INVENTION

[0018] The present invention relates to a chemical sensor, sensingsystem and sensing and identification method which provide for amulti-sensor, cross-reactive, sensor array having a rapid response time,a rapid sampling time, dynamic modulation of sampling and detectionparameters, intelligent feedback control of analyte sampling conditions,smart mode sampling, smart detection through application ofsophisticated analyte detection algorithms, and high sensitivity,discrimination, and detection capability for a variety of targetanalytes at sub ppm to ppb level concentrations.

[0019] One object of the present invention is to provide a relativelyinexpensive, robust, dynamically configurable, portable sensing device.

[0020] An additional object of the present invention is to provide forporous or fibrous sensor substrates which enhance the responsivity,selectivity, and discrimination of sensors for target analytes.

[0021] A further object of the present invention is to provide forreal-time, dynamic configuration of sensor excitation sources,detectors, sampling time and sampling rate to optimize sensorresponsivity and selectivity for target analytes in a given samplingenvironment.

[0022] A yet further object of the present invention is to provide forrapid sensor response and rapid detection of low level signals formonitoring sensor temporal response profiles in detecting anddiscriminating target analytes.

[0023] A still further object of the present invention is to provide foran intelligent or “smart” nose that mimics the highly sensitive anddiscriminating vapor detection capability of olfactory systems ofanimals

[0024] An additional object of the present invention is to enablesampling under both negative and positive ambient pressure conditions.

[0025] A further object of the present invention is to provide forintelligent sensing of target analytes through electronic modulation ofsampling conditions, such as flow rate, sampling duration, and sensortemporal response profiles by way of computer-controlled feedback.

[0026] An additional object of the present invention is to provide forremovable, interchangeable sensor array substrates for rapidly changingsensor materials and sensor sites in the arrays for either targetingspecific analytes or replacing spent sensors when they lose theirresponsivity to analytes due to either photo-bleaching or chemicalreaction.

[0027] A further object of the present invention provides forutilization of a wide variety of sensor materials, such as dyes,dye-polymers, and polymers conjugated with dyes, which would normally beconsidered less suitable with conventional sensing devices due torelatively small analyte response signals.

[0028] An additional object of the present invention provides formultiple, cross-reactive sensors deployed in a sensor array fordetecting and discriminating a wide variety of target analytes incomplex sample mixtures.

[0029] Yet another object of the present invention is in providingdirectly illuminated sensors that do not require epi-illuminating opticswhich produce undesirable optical signal losses at low response levels.

[0030] A further object of the present invention is in providingreal-time response signal baseline resetting and high gain responsesignal amplification tailored to individual sensor elements to avoiddetector saturation, eliminate background fluorescence, and provide forsimultaneous sampling and discrimination with all sensor elements in thearray regardless of relative sensor responsivity to analytes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] This invention is pointed out with particularity in the appendedclaims. Other features and benefits of the present invention can be moreclearly understood with reference to the specification and theaccompanying drawings in which:

[0032]FIG. 1 is a schematic diagram comparing a mammalian olfactorysystem with the sensing system of the present invention;

[0033]FIG. 2 is a schematic diagram of the analyte detection method ofthe present invention;

[0034]FIG. 3 is a block diagram showing hardware components of thesensing system of the present invention;

[0035]FIG. 4 is a block diagram of electrical component modules of thesensing system of the present invention;

[0036]FIG. 5 is a schematic of an electrical circuit of the lightgeneration module of the present invention;

[0037]FIG. 6a is a schematic diagram of an inhale configuration for thesample delivery module of the present invention;

[0038]FIG. 6b is a schematic diagram of an exhale configuration for thesample delivery module of the present invention;

[0039]FIG. 7 is a schematic of an electrical control circuit for thesample delivery module of the present invention;

[0040]FIG. 8 is a schematic diagram of a sample detection chamber of thepresent invention;

[0041]FIG. 9 is a schematic of an electrical circuit of the preamplifiermodule of the present invention;

[0042]FIG. 10 is a schematic of an electrical circuit of the amplifiermodule of the present invention;

[0043]FIG. 11 is a schematic of the electrical circuit connecting thechannel output lines from the amplifier and input lines of the A/Dconverter in the microcontroller computer;

[0044]FIG. 12 is a schematic of an electrical circuit for themicro-computer control module of the present invention;

[0045]FIGS. 13a-b are schematic diagrams showing a typical sensor arraymodule configuration for the sensor of the present invention;

[0046]FIG. 14 is a schematic of a data acquisition timing diagram usedin the sensing method of the present invention;

[0047]FIG. 15 is a schematic flowchart of a sensor training methodemployed in the sensing method of the present invention;

[0048]FIG. 16 is a schematic flowchart of an analyte test methodemployed in the sensing method of the present invention;

[0049]FIGS. 17a-d show comparative changes in fluorescent sensorresponse to methanol, amyl acetate, acetone and dinitrobenzene analyteswith conventional glass sensor substrates and innovative sensorsubstrates of the present invention;

[0050]FIG. 18 shows comparative changes in fluorescent sensor responseto saturated DNT explosive analyte with conventional glass sensorsubstrates and an innovative sensor substrate of the present invention;

[0051]FIGS. 19a-b show comparative changes in fluorescent sensorresponse to methanol samples at various analyte concentrations with aconventional glass sensor substrate and an innovative sensor substrateof the present invention;

[0052]FIG. 20 show time-sensor contour plots of fluorescence intensityfor a nine element sensor array of the present invention when exposed tovarious analytes;

[0053]FIG. 21 is a schematic flowchart of the sensor training methodemployed in the smart sensing method of Example 3;

[0054]FIG. 22 is a schematic flowchart of the analyte test methodemployed in the smart sensing method of Example 3;

[0055]FIGS. 23a-d are plots of sensor fluorescence responses to acetoneand air target analytes with short and long sniffs when using the smarttraining method of Example 3;

[0056]FIGS. 24a-e are plots of typical sensor fluorescence responses ofDow and cellulose-alumina sensors in a fiber optic sensor array tosaturated and unsaturated methanol analyte;

[0057]FIGS. 25a-d are plots of typical sensor fluorescence responses ofa Dow sensor in a fiber optic sensor array to saturated and unsaturatedamyl acetate and xylene; and

[0058]FIGS. 26a-c are plots of typical sensor fluorescence responses ofDow sensor in the sensor and sensing system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0059] The conceptual basis of the intelligent sensing device and methodof the present invention has evolved from studies of biologicalolfactory systems in which an artificial intelligent sensing system hasbeen developed which provides for cross-reactive sensor arrays tailoredto address design issues such as how odors are presented, how thesensing sites are deployed, how the changes in fluorescence areevaluated over time and space, how the analytical circuits are designed,how the data are stored and interpreted, and how pure compounds andmixtures are detected and identified.

[0060] I. Overview

[0061]FIG. 1 is a schematic diagram comparing a mammalian olfactorysystem with the sensing system of the present invention. In theperipheral olfactory circuit shown at the top of FIG. 1, many thousandsof parallel channels of distributed olfactory sensory neurons(“Detection/Transduction”) in the nasal cavity, into which odors aredrawn by inhalation, extend convergent axonal projections(“Transmission”) to the glomeruli of the olfactory bulb (“Integration”).Periglomerular neurons (“pg”) are inhibitory interneurons that connectthe glomerulli with one another and modulate mitral/tufted neurons(“M/T”) cell activity . The M/T have dendrites extending from theglomeruli to their cell bodies and give rise to axons that leave theolfactory bulb. Granule neurons (“grl”) are inhibitory interneurons thatmodulate M/T cell activity.

[0062] The innovative sensing method and sensing device design of thepresent invention mimics and parallels the structure and operationalcharacteristics of the mammalian olfactory system through thecombination of electro-optical hardware component modules,microprocessor control and software sampling and detection algorithms.In the artificial nose embodiment shown in FIG. 1, the sample cavitydesign mimics the mammalian nasal cavity where odors (i.e. vaporanalytes) are drawn into the sensing module (“sniffed” or “inhaled”) andtheir interaction with a plurality of sensing elements (“sensoryneurons”) in a sensor array triggers an external event. In oneembodiment, the analyte interaction with sensing elements producesemitted light energy at a detectable characteristic wavelength when thesensor elements are illuminated by excitation light energy from afiltered LED array. The multi-element sensor array of the presentinvention thus mimics the sensory neurons of the olfactory system inresponding to the external triggering event, emitted light energysignaling the presence of an analyte, and detecting this triggeringevent by way of a filtered photodiode array (“Detection”). Thephotodiode preamplifiers mimic an olfactory sensory neuron by convertingthe optical signal to an electrical voltage signal (“Transduction”)which amplified, manipulated and transported via electrical circuits(“Transmission”) to an analog-digital (“A/D”) converter and a softwarecontrolled microprocessor for data manipulation, analysis, feedbackcontrol, detection and identification (“Integration”). These featuresare replicated for each sensor element in the array. While theembodiment shown in FIG. 1 provides for 32 array element channels, thepresent invention provides for configuring the array with virtually anynumber of array elements and channels. Thus, the sensor array of thepresent invention may be expanded or contracted without limit by addingor removing elements and channels according to the requisite analytedetection, discrimination and identification needs of an specificsampling application.

[0063]FIG. 2 provides an overview of the analyte sensing and detectionmethod of the present invention. Ambient odors (analytes) are sniffed(transported to the sensor array) where the odors interact with thearray sensor elements. Light energy excitation of the sensor elements inthe presence of the odors produces a detectable optical response signaldue to emitted light produced by analyte interaction with the dyes ordye-polymer compounds in the sensor elements. The spatio-temporaloptical response of the array to the odor is detected, recorded,manipulated, and then matched to known target odors via smart analyticalalgorithms which apply either pattern matching, neural network, neuronalnetwork, or statistical analysis methods to detect, discriminate andidentify the odor.

[0064] The hardware and software components and configuration of theinnovative sensor of the present invention provide for an compact,portable, inexpensive, expandable, rapidly responding sensing devicethat can modify its detection strategy on the fly. The innovative designand method provides for real-time, on-the-fly, modulation of: a) theoutput of light emitting diodes (LEDs), such as wavelength, intensity,and frequency; b) the detection properties of photodiodes, such aswavelength, gain, and frequency; c) the sampling parameters, such asfrequency, duration, number, velocity, and rise-fall dynamics; and d)sampling time constant or temporal filter settings, for dynamicallyresponsive, smart feedback control in sampling, detection andidentification of analytes.

[0065] In addition to dynamic response modulation, the device and methodfurther provide for hardware and algorithm implementations whichevaluate the synchrony and noise characteristics across differentsensors, especially those of the same composition being examined atdifferent wavelengths. This provides a powerful tool for identifying andutilizing small response signals and rejecting noise.

[0066] By providing for independently illuminated, detected, recorded,and modulated sensing channels, levels of flexibility, expandability,portability, efficiency, and economy are achieved that are difficult torealize with conventional sensor designs, light sources, filteringsystems, and light detectors. In addition, the use of small,inexpensive, flexibly programmable, computational microcomputerplatforms and interchangeable sensors and sensor array modules providesfor increased flexibility and tailoring of sensor performance andcapabilities to real world sensing applications.

I. Sensors

[0067] In the sensing device of the present invention, analytes (odors)drawn in and out of the sensing chamber are detected by the fluorescencechanges produced by their interaction with sensor elements duringirradiation of the sensors with excitation light in the presence of theanalytes. For optical sensors which rely on light excitation, absorptionand emission, the selection of analyte detection and discriminating dyeindicators is important to the design and performance characteristics ofa cross-reactive sensor array. An important requirement of candidate dyematerials for optical sensor elements is that they produce acharacteristic optical response signature in the presence of targetanalytes. The sensing effect of the dye materials may be based on lightfluorescence, absorption, luminescence, phosphorescence,electroluminescence, or other methods for modulation of photonicemission by chemical compounds, such as polymers. These photonicmeasures may also be dependent on the physical and chemical propertiesof the substrate, or the presence of additional dye materials.

[0068] Typically, for cross-reactive sensor arrays, it is preferable toprovide sensor array elements formed from dye materials with differentresponse spectra, different analyte sensitivities, and different analytediscrimination characteristics so as to provide broad spectral detectionand discrimination for a variety of analytes. Sensor elements may becomprised of neat dyes, dye compounds, for example conjugated dyes, ordye-polymer mixtures which produce characteristic optical responses toanalytes of interest. Sensor materials are generally applied, deposited,or deployed on substrates in the form of fluids, gels, slurries, thin orthick film coatings, beads, droplets, spots, protrusions, fibers,sheets, and other shapes having complex surface textures or protrusions,including fibrilated or hair-like structures.

A. Dye Materials

[0069] Generally, any dye that provides a detectable characteristicoptical response signature to an analyte at ultraviolet, visible orinfrared wavelengths may be employed. Different dye materials mayrequire different excitation and emission wavelengths, which can beaccommodated simultaneously in the sensing device of the presentinvention by appropriate matching LEDs, photodiodes, and light filterswavelengths to required dye wavelengths. In a preferred embodiment,sensors are comprised of a fluorescent dye material applied to a porousor fibrous substrate material.

[0070] In a preferred embodiment, dye candidate materials which can beeasily applied to and adhere to the innovative fibrous sensor substratesof the present invention are desired. In alternative embodiments, wheredye-polymer materials are employed, dye candidates that can be readilyincorporated into polymer matrices and whose optical responsecharacteristics are modified by the polymer are desirable. In oneembodiment, at least one dye is incorporated into the polymer sensormatrix either by reacting the dye with the polymer to form a dye-polymercompound, or by physically combining the dye and polymer to form acomposite mixture of the two materials. In an alternative embodiment,conjugated dyes, such as acryloyl fluorescein and others, may beutilized where it is desirable to incorporate the dye directly into thepolymer sensor material by way of covalent bonding.

[0071] While the sensor dye may be either a chromophore-type or afluorophore-type, a fluorescent dye is preferred because the strength ofthe fluorescent signal typically provides a better signal-to-noise ratioand improves detection of target analytes. In the most preferredembodiment, polarity-sensitive dyes or solvatochromic dyes are utilized.Solvatochromic dyes are dyes whose absorption or emission spectra aresensitive to and altered by the polarity of their surroundingenvironment. Typically, these dyes exhibit a shift in peak emissionwavelength due to a change in local polarity. Polarity changes whichcause such wavelength shifts can be introduced by the polymerized matrixused for a particular sensor family, by the presence of a targetanalyte, or by the combination of the polymer matrix and analyteinteraction with the dye. The change in polarity creates acharacteristic optical response signature which is useful for detectingspecific target analytes. One preferred solvatochromic dye is Nile Red,available from Eastman Kodak (Rochester, N.Y.). Nile Red exhibits largeshifts in its emission wavelength peak with changes in the localenvironment polarity. In addition, Nile Red is soluble in a wide rangeof solvents, is photochemically stable, and has a relatively strongfluorescence peak. Alternatively, other solvatochromic dyes such asProdan, 6-propionyl-2-(N,N-dimethylamino)napthalene, or Acrylodan,6-acryloyl (dimethylamino) napthalene, available from Molecular Probes(Eugene, Ore.), may be employed.

[0072] Additional dyes which are conventionally known in the art and maybe used as dyes in the present invention are those found in Tables 3-7and Table 11 of U.S. Pat. 5,512,490 to Walt and Kauer which isincorporated herein by reference. A particularly useful reference forselection of candidate dyes such as metallochromic indicators, includingazo and triphenylmethane dyes, and fluorescent indicators, which may beeither mixed with or conjugated with polymers to form sensors of thepresent invention, is Indicators [E. Bishop (ed.), Pergamon Press (NewYork 1972)] which is incorporated herein by reference. Anotherparticularly useful reference for selecting appropriate dye indicatorsis the most recent edition of R. P. Haugland, Handbook of FluorescentProbes and Research Chemicals (₆th ed.), Molecular Probes Inc.(Eugene,Ore., 1996) which is herein incorporated by this reference.

B. Dye-polymer Sensors

[0073] Diverse families and types of optical sensor elements may befabricated as sensors and sensor arrays of the present invention byincorporating sensor dyes, such as metallochromic indicators,fluorescent indicators, or solvatochromic dyes, within various polymermatrices. By combining dyes with different polymers, or combiningpolymers with different dyes, a wide variety of sensor materials may beproduced which exhibit differential sensitivity to analytes (see J.White, et al., Anal. Chem., 68:2191-2202(1996)). By incorporating suchdyes in sensor elements made from different polymer matrices of varyingpolarity, hydrophobicity, pore size, flexibility and swelling tendency,unique sensors are produced that react differently with molecules ofindividual analytes, giving rise to distinguishable and characteristicfluorescence responses when exposed to target analytes. Since theresulting sensor materials may have different excitation and emissionwavelengths, LEDs, photodiodes, and excitation and emission filterwavelengths must be appropriated adjusted to match sensor requirements.

[0074] 1. Polymer Selection

[0075] A variety of polymer sensor chemistries may be utilized infabricating a wide diversity of dye-polymer sensor materials accordingto the method of the present invention. By way of example, a monomer oroligomer may be selected from any member of the group of condensationpolymers derived from such monomers as alcohols, dialcohols, amines,diamines, esters, diesters, carboxylic acids, dicarboxylic acids, diacidchlorides, carbonates, anhydrides, amides, imides, benzoxazoles,benzthiazoles, benzimidazoles, quinozalines, aromatic compounds,including specific polymers such as phenol-formaldehydes,urea-formaldehydes, melamine-formaldehydes, acetyl compounds, lactones,nylons, or polyesters. Alternatively, a monomer may be selected from anymember of the group of step-type reaction polymers comprising sulfones,ethers, phenylene oxides, phenylene oxide ethers, Diels-Alder-typereactants, urethanes and arylenes. Monomers may alternatively beselected from any member of the group of vinyl polymers comprisingethylenes, vinyl chlorides, vinylidene chlorides, tetrafluoroethylenes,acrylonitriles, acrylamides, acrylates, methacrylates, acetates,styrenes, methyl styrenes, vinyl esters, vinyl pyrrolidones, butylenesand butadienes.

[0076] For optical sensors, sensor elements are typically selected basedon distinguishable differences in their characteristic optical responsesignatures when illuminated by excitation light energy in the presenceof a target analyte. In fabricating polymer sensor arrays, polymersensor elements are selected which have characteristic optical responsesignatures when mixed with a dye compound and illuminated by excitationlight energy in the presence of a target analyte. Thus, preferredoptical sensor materials for sensor arrays are selected based on bothphysical and chemical differences in sensor types which, in combinationwith a reporter dye compound, produce a characteristic optical responsesignature in the presence of the analyte when illuminated by excitationlight energy.

[0077] The following monomer, polymer and copolymer compositions andtheir derivatives would be particularly useful as candidate polymermaterials for dye-polymer optical sensors of the present invention:polyethylene glycol, polycaprolactone, polyarylamide, methylmethacrylate [MMA], 2-hydroxyethyl methacrylate, siloxane,dimethylsiloxane, acrlyamide, methylenebisacrylamide [MBA], poly(1,4-butylene) adipate, poly (2,6-dimethyl-1,4-phenyleneoxide) [PDPO],triethoxysilyl-modified polybutadiene (50% in toluene) [PS078.5],diethoxymethylsilyl-modified polybutadiene in toluene [PS078.8],acryloxypropylmethyl-cyclosiloxane [CPS2067], (80-85%) dimethyl-(15-20%)(acryloxypropyl) methylsiloxane copolymer [PS802],poly(acryloxypropyl-methyl)siloxane [PS901.5], (97-98%) dimethyl-(2-3%)(methacryloxypropyl)methylsiloxane copolymer [PS851],poly(acrylonitrile-butadiene-styrene)[PABS], poly(methyl methacrylate),poly(styrene-acrylonitrile 75:25) [PSAN],acryloxypropylmethylsiloxane-dimethylsiloxane copolymer, methylstyrenes,styrenes, acrylic polymers, and methylstyrene divinyl benzene.

[0078] 2. Polymerization Initiators

[0079] In fabricating dye-polymer sensors of the present invention,polymerization of prepolymer mixtures of desired monomer combinationsmay be achieved by thermal polymerization, condensation polymerization,photoinitiated polymerization, or either crystallization orprecipitation from solution followed by annealing.

[0080] In one preferred embodiment, thermal polymerization may beutilized either with or without the addition of an initiator. In oneembodiment, initiators may be employed to control the rate of thermalpolymerization. Since it is often desirable to carry out polymerizationof monomer mixtures at low temperature to prevent side reactions, theselection of thermal initiators is generally restricted to organicperoxides, such as dialkyl peroxides or diacylperoxides, organichydroperoxides, azo compounds, such as azobisisobutyronitrile, andorganometallic reagents, such as silver alkyls. Alternatively, thermalinitiation may be accomplished by redox agents, for example, in aqueoussolutions, a persulfate salt used in combination with a bisulfite ionreducing agent may form an intermediate sulfate radical ion andsubsequent hydroxyl radical initiator. Similar redox reaction initiatorsmay be used by combination of alkyl hydroperoxides and a reducing agent,such as ferrous ion. Additionally, some monomers, such as styrenes,undergo free-radical polymerization when heated or exposed to excitationlight energy. Alternatively, anionic or cationic polymerizationcatalysts may also be employed.

[0081] In one embodiment, dye-polymer compound synthesis is accomplishedby way of condensation polymerization. With this method, no initiator isrequired and polymerization occurs by way of direct reaction of desiredmonomers either in the presence or absence of a catalyst to stabilize ametastable intermediate.

[0082] In one embodiment, photoinitiated polymerization is utilized. Oneadvantage of photopolymerization is that it offers greater reactioncontrol than thermal polymerization and enables spatial control of localpolymerization reactions which can be restricted to regions illuminatedby directed light energy. Photopolymerization may be conducted eitherwith or without a specific photosensitizer initiator compound. Forexample, in the absence of a specific photosensitizer, many candidatemonomer materials that can undergo chain reaction polymerization aresusceptible to photopolymerization since the absorption of lightproduces free radicals or ions. Examples of such compounds areunsaturated monomers such as vinyl alkyl ketones, vinyl bromides,styrene, methyl methacrylate and isobutylene.

[0083] In one alternative embodiment, a photosensitizer must be added tothe prepolymer mixture of monomers for photopolymerization of thepolymer. Photosensitizers are compounds that absorb light in a desiredregion of the spectrum, typically ultraviolet or visible light, andsubsequently dissociate into free radicals or transfer absorbed energydirectly to a monomer. While some thermal initiators, such as azocompounds and peroxides are also photosensitizers, many alternativeinitiators may be used as photosensitizers even though they do notdissociate thermally at useful temperatures. Examples of particularlyuseful photosensitizers are carbonyl compounds, such as acetone,biacetyl benzophenone benzoin, or α-chloroacetone, condensed ringaromatics, such as anthracene, peroxides, such as t-butyl peroxide orhydrogen peroxide, organic sulfides, such as diphenyl disulfide ordibenzoyl disulfide, azo compounds, such as azoisopropane,azobisisobutyronitrile or aryldiazonium salts, halogen-containingcompounds, such as chlorine, chloroform, carbon tetrachloride,bromotrichloromethane, bromoform or bromine, metal carbonyls, such asmanganese pentcarbonyl and carbon tetrachloride or rhenium pentacarbonyland carbon tetrachloride, and inorganic ions, such as FeOH⁺² or FeCl₄ ⁻.In one preferred embodiment, benzoin ethyl ether initiator is utilized.

C. Substrates

[0084] The present invention provides array sensor element compositionsdisposed on substrates which may be either inert or active duringanalyte sampling and detection. While inert supports are typically usedin conventional sensing devices, the present invention provides foractive dye support materials that enhance sensor responses to specificanalytes by their unique chemical, physical, adsorption, or opticalcharacteristics. Different substrate support materials may be employedwithin a single array where specific support materials are matched tospecific dyes, dye compounds and dye polymer mixtures to produceenhanced sensor responses to specific analytes.

[0085] An important innovation in the present inventions is thedevelopment of fibrous substrate supports which enhance sensor responsesignals for a variety of dye materials, such as neat dyes, dyecompounds, and dye-polymer mixtures. As shown in FIGS. 17a-d, FIG. 18,and FIG. 19a-b, substantial sensor response enhancements have beenachieved with the innovative fibrous supports of the present invention.

[0086] An additional advantageous feature of the present invention is inproviding for removable or interchangeable arrays, array substrates, orsubstrate supports to facilitate changing sensor arrays to matchspecific analyte sampling and detection requirements. In one embodiment,multiple layers of array substrates may be employed for diversificationand enhancement of sensor detection capabilities for identifying bothbroad and specific classes of analytes.

[0087] One skilled in the art would recognized that it is generallypreferred to position sensor substrates at the appropriate viewing angleand distance from light emitting diode excitation light sources andphotodiode detectors so as to provide for optimum sensor signalgeneration and detection. In one preferred embodiment, a separatesubstrate holder may be provided for positioning and securing arraysubstrates. In an alternative preferred embodiment, the sample chamberhousing may be configured for proper positioning and securing arraysubstrates.

1. Conventional Substrates

[0088] As will be appreciated by those in the art, the number ofpossible substrate materials are very large, and include, but are notlimited to, glass and modified or functionalized glass, plastics(including acrylics, polystyrene and copolymers of styrene and othermaterials, polypropylene, polyethylene, polybutylene, polyurethanes,teflons, etc.), polysaccharides, nylon or nitrocellulose, resins, silicaor silica-based materials including silicon and modified silicon,carbon, metals, inorganic glasses, plastics, and a variety of otherpolymers.

[0089] In preferred embodiments, optically transparent substrates areemployed to permit placement of the substrate between LED light sourcesand photodiode detectors as shown in FIGS. 6a-b and FIG. 8. Inalternative embodiments, where the LEDs and photodiodes are placed onthe same side of the substrate, optically opaque or optically absorbing,reflective, and scattering materials may be employed.

[0090] Where conventional flat, planar, curved or non-planar solidsensor substrates are used, these substrates are generallyself-supporting and substrate supports are not required but may beoptionally employed.

2. Signal Enhancing Sensor Substrates

[0091] While conventional flat, planar, or curved non-planar solidsensor substrates may be employed, increased sensor surface area canarise from depositing dyes on highly convoluted surfaces that includefine fibrous hairs of different materials, particulates, poroussubstrates, or films and substrates suspended within the samplingstream. With the innovative substrates of the present invention, thesepreferred substrate embodiments provide enhanced contact and interactionbetween sample target analytes and sensor elements, increased opticalresponse signal per unit of sensor geometrical surface area, andincreased optical response signal per unit of sensor volume.

[0092] In preferred embodiments, highly permeable, high surface area,textured, fibrous or particulate substrates which have substantial openporosity for unimpeded transport of vapors and fluids are desired. Inpreferred embodiments, single or multi-ply layers of papers, felts,laid, or woven fibrous materials or fabrics are employed. In alternativeembodiments, loosely packed individual fibrous or particulate materialsmay be employed.

[0093] In a most preferred embodiment, fibrous substrate materials areemployed for signal enhancement. Important considerations in selectingfibrous substrates are substrate permeability to vapors, high accessiblesurface area per unit volume, response signal enhancement for specificanalytes, how the substrate interacts with the sample flow to provideopen access of its external and internal surfaces to analytes forinteraction with the sensing material. While particularly useful fibersubstrates are porous, lightweight paper or tissue products, for exampleKimwipe™ (Kimberly-Clark Corp., Roswell, Ga.), lens papers, facialtissues, and products made from cotton, rayon, glass, and nitrocellulosefibers, other fibrous materials employing natural or synthetic fiberssuch as felt, batting, textiles, woven fabrics, yarns, threads, string,rope, papers, and laminates or composites of such materials would beequally suitable as long as they possess the requisite fluidpermeability, surface area, surface area to volume ratio, and openporosity for free transport of vapor and fluid analytes.

[0094] Particularly useful inorganic fibers and fibrous materialcompositions are natural and synthetic fibers made from glass, ceramic,metal, quartz, silica, silicon, silicate, silicide, silicon carbide,silicon nitride, alumina, aluminate, aluminide, carbon, graphite, boron,borate, boride, and boron nitride. Particularly useful natural orsynthetic fibers and fibrous material compositions are polymer fibersmade from aromatic polyamides, nylons, polyarylonitrile, polyesters,olefins, acrylics, cellulose, acetates, anidex, aramids, azlon,alatoesters, lyocell, spandex, melamines, modacrylic, nitrile,polybenzinidazole. polyproplylene, rayons, lyorell, sarans, vinyon,triacetate, vinyl, rayon, carbon pitch, epoxies, silicones, sol gels,polyphenylene-benzobis-ozazole, polyphenylene sulfides,polytetrafluoroethylene, teflon, and low density or high densitypolyethylene. In one preferred embodiment, fiber materials that arehighly absorbent and have good dye retention characteristics, forexample the cellulosic fiber known as Lyorell, may be employed.

[0095] In alternative embodiment, fibers may be coated with eitherchemical sizing, polymer, ceramic or metallic materials. Chemical sizingsuch as modified polyvinyl acetates, organosilanes, coupling agents,anti-static agents and lubricants may be employed as appropriate.

3. Chemically-modified Substrates

[0096] In alternative embodiments, the sensor substrates of the presentinvention may be chemically or physically modified to enhance surfacearea, absorption, adhesion, hydrophobicity, hydrophilicity, repulsion,discrimination or specificity. In some embodiments, the substrate my bechemically altered to provide chemical functionality for interactionwith analytes, such as providing for enhanced affinity, enhancedrepulsion, or steric impediments to analyte adsorption.

D. Sensor Fabrication

[0097] As discussed above, sensors may be fabricated from neat dyes, dyepolymer compounds, such as intrinsically fluorescing dyes or conjugateddyes, or dye-polymer With respect to signal enhancing sensor substrateproperties of the present invention, one skilled in the art wouldgenerally recognize and understand the intended meaning of the term“textured” generally referring to material surfaces which typically havea distribution of surface topographical features, such as high points(peaks) and low points (valleys), ranging from +/−100 nm to +/−1000 umRMS, the term “high permeability” generally referring to materials andmaterial structures with a high open porosity that provide essentiallyfree, unimpeded access and convective or diffusive transport to lowviscosity fluids, the term “high surface area” generally referring tomaterials that have a surface area of at least 1 M²/g and typicallyrefers to surface areas ranging between 2 to 500 M²/g, the term “highsurface area to volume” generally referring to materials having asurface area to volume ratio of at least 1 M²/cm³ and typically refersto surface area to volume rations ranging between 2 to 1000 1 M²/cm³,the terms “porous” or “porosity” generally referring to materials havinga distribution of pore sizes ranging from 100 nm to 1000 um, and theterm “high open porosity” generally referring to materials whose poredistributions substantially comprise open pores. mixtures applied toconvention substrate surfaces or the innovative fibrous substrates ofthe present invention Neat dye and dye-polymer sensor recipes for thesensors used in Examples 1 and 3 are provided below. Recipes for thesensors used in Examples 2 and 4 are provided elsewhere [see J. White,et al., Anal. Chem. 68(13):2191-2202 (1996) which is incorporated hereinby this reference].

1. Neat Dye Sensors

[0098] A Nile Red/chloroform solution is prepared by dissolving 1 mg ofNile Red per 1 ml of chloroform. Fiber substrate sensors are typicallyfabricated by applying approximately. 0.2 mL of dye solution evenly overa 3 cm×3 cm area of substrate material. The solvent is allowed toevaporate, leaving the fibers of the substrate coated and infiltratedwith dye. A sensor element is prepared by cutting an approximately 4mm×4 mm piece of dyed substrate to cover the face of a photodiode. Atemplate representing the photodiode array configuration and photodiodeplacement is used to position the sensor element on a glass cover slip.The sensor is then held in place by taping the edges. Other methods ofsecuring the sensor are also possible, such as employing glue ormechanical clamping.

2. Dye-Polymer Mixtures

[0099] Typically, a sensor made from a dye-polymer mixture is producedby mixing Nile Red solvent solution with a monomer solvent solution.Generally, in preparing sensors from dye-monomer solution mixtures, itis preferable to minimize monomer content and maximize dye content toprovide maximum sensor response signal. However, with some analytes,additional monomer is added to provide optimum sensor response signal.The upper limit of monomer additions is generally established byviscosity considerations where low viscosity solutions are desired forapplication of thin sensor layers or coatings to substrates. While mostmonomer solutions are prepared with chloroform solvent, some monomersrequire other solvents such as methanol and toluene.

[0100] Nile Red/polyethylene oxide (PEO) sensors are prepared from asolution of 0.007 g of polyethylene oxide dissolved in 1 mL ofchloroform. A Nile Red/chloroform solution is prepared by dissolving 1mg of Nile Red per 1 ml of chloroform. 0.01 ml of the Nile Red solutionis added to 1 ml of the monomer solution.

[0101] Nile Red/Poly(N-vinylpyrrolidone sensors are prepared from asolution of 0.062 g of monomer [PolySciences, Inc., Warrington, Pa.]dissolved in 1 mL of chloroform. A Nile Red/chloroform solution isprepared by dissolving 1 mg of Nile Red per 1 ml of chloroform. 0.01 mlof the Nile Red solution is added to 1 ml of the monomer cellulosesolution.

[0102] Nile Red/Poly (ethyl cellulose) sensors are prepared from asolution of 0.025 g of ethyl cellulose [PolySciences, Inc.] is dissolvedin 1 mL of a 4:1 mixture of toluene and ethanol. A Nile Red/toluenesolution is prepared by dissolving 1 mg of Nile Red per 1 ml of toluene.0.01 ml of the Nile Red solution is added to 1 ml of the monomersolution.

[0103] Nile Red/Poly (dimethylsiloxane) sensors are prepared from asolution of 1 mL of Poly(dimethylsiloszane) 200 (R) fluid (1000 cPviscosity) [Aldrich Chemical Co., Milwaukee, Wis.] dissolved in 0.5 mlof toluene. A Nile Red/toluene solution is prepared by dissolving 1 mgof Nile Red per 1 ml of toluene. 0.01 ml of the Nile Red solution isadded to 1 ml of the monomer solution.

[0104] PBA sensors are prepared from a solution of 0.4 g ofpoly(1,4-butylene adipate) in 1 ml of chloroform to which 0.2 ml of NileRed chloroform solution (1 mg/ml) is added.

[0105] Pentiptycene-derived phenylenecthynylene polymer 1 [SeeYang andSwager in J.Am.Chem.Soc. 120:11864-11873(1998)] sensors areintrinsically fluorescent and do not require dye additions. Thesesensors are prepared from a solution of 1.2 mg of polymer in 1 mL ofchloroform.

[0106] For each of the above sensor compositions, sensors are preparedon conventional substrates by applying approximately. 0.2 mL of themonomer or polymer solution mixture evenly over a 3 cm×3 cm area of aglass substrate The solvent is allowed to evaporate, leaving thesubstrate coated with dye. The polymer is cured at room temperature.

[0107] Fiber substrate sensors are typically fabricated by applyingapproximately. 0.2 mL of dye, dye-polymer, or fluorescent polymersolution evenly over a 3 cm×3 cm area of substrate material. The solventis allowed to evaporate, leaving the fibers of the substrate coated andinfiltrated with dye. The polymer is cured at room temperature. A sensorelement is prepared by cutting an approximately 4 mm×4 mm piece of dyedsubstrate to cover the face of a photodiode. A template representing thephotodiode array configuration and photodiode placement is used toposition the sensor element on a glass cover slip. The sensor is thenheld in place by taping the edges. Other methods of securing the sensorare also possible, such as employing glue or mechanical clamping.

[0108] Dow/Alumina sensors are prepared from a solution of 0.062 g ofdimethyl siloxane dispersion coating (Dow Corning, Midland, Mich.)dissolved in 2 ml of toluene. A Nile Red/toluene solution is prepared bydissolving 1 mg of Nile Red per 1 ml of toluene. 0.05 ml of the Nile Redsolution is added to 1 ml of the monomer solution.

[0109] PDPO/Alumina sensors are prepared from a solution of 0.2 g ofpoly(2,6-dimethyl-1,4-phenyleneoxide) (Aldrich Chemical, Milwaukee,Wis.) dissolved in 1.5 ml of chloroform. A Nile Red/toluene solution isprepared by dissolving 1 mg of Nile Red per 1 ml of toluene. 0.375 ml ofthe Nile Red solution is added to 1 ml of the monomer solution.

[0110] PC/Alumina sensors are prepared from a solution of 0.19 g ofpolycaprolactone (2,6-dimethyl-1,4-phenyleneoxide) (Aldrich Chemical)dissolved in 1.5 ml of chloroform. A Nile Red/toluene solution isprepared by dissolving 1 mg of Nile Red per 1 ml of toluene. 0.05 ml ofthe Nile Red solution is added to 1 ml of the monomer solution.

[0111] For each of the above polymer/alumina sensor compositions,sensors are prepared on conventional substrates with alumina poweradditions. 150 mesh alumina powder (Aldrich Chemical) is treated with a1 mg/ml solution of Nile Red in toluene. The alumina is washed intoluene to remove excess dye and allowed to dry overnight. A droplet ofthe dye-monomer-solvent solution is applied to a glass coverslipsubstrate and the Nile Red stained alumina powder is sprinkled over themonomer solution droplet. The monomer-alumina mixture is thenpolymerized at room temperature.

[0112] The Celluse/Alumina/Cellulose fiber optic sensors described inExample 4 are prepared from the ethyl cellulose solution describedabove. Fiber ends were dipped in the ethyl cellulose preparation,allowed to air dry for 1 min, and dipped in the Nile Red treated aluminapowder. After air drying for 1 min, the fiber was dipped in the ethylcellolose solution again and air cured.

[0113] The PC/PSAN/Alumina fiber optic sensors described in Example 4are prepared from a 0.2 ml solution of 0.2 g of polycaprolactonedissolved in 2.0 ml of chloroform and a 0.2 ml solution of 0.2 g of polystyrene-acrylonitrile dissolved in 2.0 ml of chloroform. A fiber end isdipped in the polymer mixture, allowed to air dry for approximately 1min, and then dipped into the Nile Red treated alumina powder (seeabove) and cured at room temperature.

[0114] The Cellulose/PDPO/Beads fiber optic sensors described in Example4 are prepared from a 0.2 ml solution of 0.2 g of poly(2,6-dimethyl-1,4-phenyleneoxide) (Aldrich Chemical) dissolved in 1.5 mlof chloroform and a 0.2 ml solution of the ethyl cellulose solutiondescribed above. The beads were 80-100 mesh alumina stained with a 1mg/1 ml solution of Nile Red in toluene and washed in toluene. A fiberend is dipped in the polymer mixture, allowed to air dry forapproximately 1 min, and then dipped in the treated alumina beads andcured at room temperature.

[0115] The RMS-044 fiber optic sensors described in Example 4 areprepared from a solution of 0.746 g of 4-6% (methacryloxyproply)methyl-siloxane, dimethyl siloxane copolymer (United Chemical Tech.) in1.8 ml of chloroform to which 60 mg of BEE photoinitiator is added. Afiber end is dipped in the polymer solution and the polymer isphoto-polymerized by exposing the fiber end to 4500 mW/cm² ofultraviolet light for 17 seconds. The photo-polymerization method wasdescribed previously [see J.White, et al., Anal. Chem. 68(13):2191-2202(1996)].

[0116] The PS901.5 fiber optic sensors described in Example 4 areprepared from a solution of 0.5 ml poly(acryloxxypropylmethl) siloxanein 0.5 ml of chloroform to which 20 mg of BEE photoinitiator is added. Afiber end is dipped in the polymer solution and the polymer isphoto-polymerized in the same manner as the RMS-044 sensor above.

[0117] The PS802/PS901.5 fiber optic sensors described in Example 4 areprepared from a solution of 0.6 ml of (80-85% dimethyl (15-20%)acryloxypropyl) methylsiloxane copolymer in 0.4 ml of chloroform towhich 60 mg of BEE initiator is added. 0.1 ml of this solution is mixedwith 0.1 ml of the PS901.5 solution (see above) and a fiber end isdipped in the copolymer solution. The copolymer mixture isphoto-polymerizeds in the same manner as the RMS-044 sensor above exceptthe exposure time was 20 seconds.

II. Sensing System

[0118] The innovative sensor and sensing system of the present inventionprovides for a rapidly responding, relatively inexpensive, dynamicallyconfigurable, intelligent, portable artificial sampling device.Innovative features of the device and method of the present inventioninclude innovative sensor substrates for enhancing response signals,improved analyte sensitivity and discrimination, real-time ambientenvironment sampling, smart training and sampling modes, andintelligent, real-time modulation and control of the sampling anddetecting methods and hardware components for adaptive learning andoptimization of sampling conditions for specific sampling environmentsand target analytes.

[0119] The innovative device delivers analytes (odors) in a controlled,pulsatile manner (sniff) to fluorescence-based sensor array and detectorarray system that generates analog electrical signals. The number ofsensors, detectors, and sampling time points are arbitrary and can bemade larger or smaller depending on the classes of analytes that arebeing targeted for detection. These analog signals are amplified andfiltered by a pre-amplifier/amplifier module and digitized to 12 bits byan analog/digital conversion module for storage in a computer memorymodule. All attributes of the sensing process, including odor delivery,sampling, analysis, detection and identification are under programmablesoftware control via a computer.

[0120] The sensing device must be trained in order to recognize specificanalytes. Training consists of delivering a known set of variousanalytes to the device, one analyte at a time, and storing matrices ofvalues that are a spatio-temporal signatures of each analyte in memory.When an unknown fluid is to be sampled after training, it is deliveredto the device and a matrix of values acquired from the unknown iscompared to matrix templates for the variety of analytes stored inmemory during the training phase. The best match between the unknown andthe library of stored matrices is then determined using a number ofdifferent algorithms. In one embodiment, the algorithm looks for thebest match after calculating the sum of the squared differences betweeneach point in the stored and unknown matrices.

[0121] The sensing system provides output results in a variety formatsincluding, but not limited to screen displays, plots, printouts,database files, and synthesized voice messages. A typical sensor outputis shown in FIG. 20 where a plot of the unique spatio-temporalfluorescence responses of the array sensors to various analytes isprovided.

A. Device Overview

[0122] The sensing device of the present invention comprises a samplingchamber housing an analyte delivery system and a multi-channel arraycomprising light emitting diodes (LEDs) focussed through an array ofexcitation filters onto individual sensor elements of a sensor array. Anarray of photodiodes, filtered with an array of emission filters,detects emitted light energy produced by illuminating the sensorelements with LED excitation light during interaction with analytes thatare drawn into the sample chamber by the analyte delivery system. Theambient temperature, humidity, and particulate levels in the samplechamber may be controlled for improved reproducibility in sampling undera variety of environmental conditions. The changes in emitted lightdetected by the photodiode array for each sensor element are digitizedby either 12 bit or, alternatively, 24 bit analogue-to-digitalconverters and stored in a computer memory module. Analyte sampling,detection, and identification are controlled by a programmablemicrocontroller directed by smart sampling and detection algorithms. Thedevice provides for fast, high gain, low noise, real-time sampling,detection and identification of a variety of vapor analytes with highsensitivity and low detection limits, typically in the sub ppm to ppbconcentration range. The innovative device further provides forintelligent sampling and detection through real-time, dynamic modulationof sampling conditions and detection criteria with real-time feedbackcontrol for optimizing device sensitivity, discrimination, and detectionof a variety of analytes.

B. System Components

[0123] The sensing device of the present invention provides forgenerating optimized signals for different dye/polymer combinations byusing different excitation and emission wavelengths for different sensortypes. Unlike conventional sensing devices, with the present invention,this can be achieved simultaneously while sampling the entire array ofsensing elements in parallel using an array of individualLED-sensor-photodiode sensing channels operating at appropriatewavelengths for a variety of sensor-analyte combinations.

[0124] The sensing device generally provides the basic functioncomprising analyte delivery and control (i.e. manipulation of spatialand temporal distributions; control over temperature, humidity, and dutycycle), detection by a sensor array and transduction of sensor signalsinto a manipulatable format, analysis of transduction output events, anddynamic feedback control over analyte delivery, detection and analysisfor intelligent sampling and detection and optimization of sensorsensitivity and analyte discrimination.

[0125]FIGS. 3 and 4 provide schematic block diagrams showing the generalmodular design and configuration of the sensor array and sensing systemcomponents. Details of the sample or analyte delivery module are shownschematically in FIGS. 6a-b. A detailed schematic of the sensor arrayconfiguration of LEDs, excitation filters, sensor elements, emissionfilters, and photodiodes is provided in FIG. 8. The relative locationsand configuration of LEDs, sensor elements, photodiodes, andemission/excitation filters are shown in FIG. 13. Detailed circuitschematics are provided for LED array controls (FIG. 5), analytedelivery fans and control valve controls (FIG. 7), photodiodepreamplifier module (FIG. 9), amplifier module (FIG. 10), connectionsinto analog to digital conversion module (FIG. 11), and computer controlmodule and pre-amp/amp power board (FIG. 12).

[0126] These modular components are described in detail in the followingsections.

C. Analyte Delivery 1. Overview

[0127] For reliable and reproducible sampling of ambient fluids, it isimportant to standardize sampling and sensing conditions by controllingthe delivery and presentation of analytes to the sensor array. In apreferred embodiment, the analyte deliver system provides feedbackcontrol over sample temperature, humidity, flow-rate, and the rise andfall times, duration, and frequency of analyte delivery.

[0128] One embodiment of the analyte delivery system is shown in FIGS.6a-b and FIG. 8. Generally the sensing chamber consists of a rectangulartube through which the analyte vapor passes. The sensing array withopposed light emitting diode light sources and photodiode photodetectorswith sensor elements is placed within a sample chamber. In thisconfiguration the incoming fluid stream generated by a gated negativepressure (i.e. a sniff pump such as a fan, pump, ‘mesopump’, bellows, ortheir equivalents) causes the fluid stream to be drawn into the sensingchamber and to be expelled to the ambient environment by the negativepressure source. In this manner, analyte vapor pulses are delivered tothe sensing array from ambient pressure sources. The sensing chamber canbe of the form of a simple tube, as described above, or may assume anyshape that may improve or optimize the delivery of the analyte pulse tothe sensor array, including complex shapes modeled after the structureof the nasal cavity of animals. In one embodiment, complex cavities withmultiple baffles are used to prevent ambient light and ambient airmovements from interfering with the generation of standardized pulses ofanalyte to the sensor array.

[0129] Generally, the sensing chamber includes: a) a means forcontrolling temperature, humidity, flowrate, rise and fall times andfrequency of the applied vapor pulses; b) a means for controlling thesurface properties of the sensing and non-sensing areas of the chamber(liquid, mucus, or gel lining) in order to impart chromatographicsurfaces to the sensing area and/or humidify, dehumidify, or distributethe analyte to the sensory surface, or to optimize response of thesensing chemistry; c) a means for aerodynamic control over chamber shapewhich may either be held constant for the duration of analyte deliveryor modulated by feedback control during analyte delivery; and d) a meansfor active, dynamic feedback control over shape, duration, flowrate,temporal envelope, and frequency of analyte sampling (sniffing). Suchfeedback may be derived from examining the spatio-temporal responsepatterns from the sensor array produced by prior analyte sampling.

2. Sensor Chamber Design

[0130] A cross-sectional view of a sampling chamber embodiment showing 9detection sites is provided in FIG. 8. In designing the samplingchamber, it was necessary to configure the chamber, sensors, LEDs andphotodiodes to comply with focal length dimensions of the integrallenses that were incorporated into the LEDs and photodiodes. Focallengths of the integral lenses were measured and, based on thesedimensions, the width of the sample chamber and the positions of thesensors within the sample chamber were arranged such that the sensorswere optimally illuminated by the LEDs and optimally observed by thephotodiodes at their respective appropriate focal distances.

[0131] The present invention provides for control over the sensingchamber environment where, for example, ambient light levels,aerodynamic flow conditions, sample humidity and temperature can bemeasured, standardized, controlled, adjusted, or modulated for differentanalyte detection tasks.

[0132] The sensing chamber can be optimized for its aerodynamicproperties by placing the detectors in cavities of various shapes. Inone embodiment, the sensors may be placed at a bend in the flow path. Inan alternative embodiment, the sensors may be located on the side of thestraight flow path. Since the present device is unique in its use ofambient flow sniffing and dynamic information gathering, the presentinvention provides an opportunity to exploit the aerodynamic propertiesof complex spaces for improved sampling performance. For example, thechamber space may be configured to mimic the actual shape of themammalian nasal cavity, or, alternatively, it may be configured toprovide preferred fluid flow or aerodynamic design features. Theseembodiments would complement the design capability of the presentinvention which provides for static and dynamic control and modulationof inhalation and exhalation during sampling.

[0133] In one embodiment, humidification of the chamber and analytesample is achieved by humidifying the incoming (inhalation) air streamin the entry nozzle and outgoing (exhalation) air stream in the exhaustpathway, both of which pass over the sensor array. In one method,humidification is accomplished by placing an absorbent material, such asfilter paper, within the air tubing. The absorbent surfaces areconnected by wicks to vials of water, thereby keeping them moist. Inalternative embodiments, the humidity of the source may also bemodulated by spraying water mist on the sampling area before sniffing.This will frequently increase the volatility of odors and improvedetectability. While other humidification methods may be employed, theprimary objective is to provide a means for balancing the humiditylevels of the ambient air with those of the analyte source. In apreferred embodiment, precise control of humidity in the chamber couldbe accomplished by using specific chamber sensors to detect humiditylevels which supply feedback to a moisture metering system.

3. Sniffing Fans and Valve System

[0134] Ambient odors are drawn into the sampling chamber (made in house)in a pulsed fashion by two continuously running fans (for example,Panaflo DC, brushless, 12 V, 270 mA, 19.7 cfm)—one for generatinginhalation (see FIG. 6a), one for exhalation (see FIG. 6b) through thesampling chamber. The inhalation or exhalation flows are gated bybutterfly valves (made in house), controlled by servo motors (Hobbico,high power, mini servo CS-35 from Tower Hobbies, PO Box 9078, Champaign,Ill. 61824-9078) governed by the computer under software control. Duringinhalation, flow from the inhalation fan is connected to the sensingchamber (via standard 1″ ID PVC plumbing materials) and flow from theexhalation fan is connected to exhaust (see FIG. 6a). During exhalation,flow from the exhalation fan is connected to the sensing chamber and theinhalation fan is connected to exhaust (see FIG. 6b). This control valvearrangement prevents the build up of pressure pulses and keeps flowrates reasonably constant for both in- and ex-halation and for rapidswitching between the two. Computer control of the servo motorsdetermines the duration, rise and fall times, and frequency of sniffing.It is important to note that these parameters (along with the othersdescribed below) can be changed in real time during data acquisition inorder to optimize the signals of interest. FIG. 7 shows the interfaceboard between the servo motors and computer.

D. Sensor Array 1. Sensor Elements

[0135] As discussed elsewhere, sensing elements are composed of eitherdye, dye compounds, or dye-polymer mixtures applied to removable sensorsubstrates. In one embodiment, thin films of either dye, dye compounds,or dye-polymer mixtures are deposited on a flat plastic or glasssubstrate. In preferred embodiments, dye, dye compounds, or dye-polymermixtures are deposited directly onto fibrous supports made from naturalor synthetic cellulose, polymers, glasses, ceramics, metallic, or othermaterials. The use of fibrous dye substrates dramatically increases themagnitude of the response signals, which improves analyte detection anddiscrimination of the device. In an alternative embodiment, thindye-polymer films or dye-containing fiber supports can be suspendedfreely across a perforated removable solid substrate which is placed inthe center of the air flow stream, thereby exposing both sides of thesensor to vapor phase analyte.

[0136] An innovative feature of the sensing device is the use ofinterchangeable, removable sensor substrates. Supporting the sensorarray on easily removable substrates, facilitates rapid changing ofsensing sites during sampling for improving the sensitivity anddiscrimination for specific analytes in a variety of samplingapplications. This feature further provides for rapid screening of dyes,dye compounds, and dye-polymer mixtures for evaluating new sensormaterials and analytical detection algorithms.

[0137] The size, thickness and surface area of sensor element sites maybe modified to optimize sensitivity and discrimination and toefficiently couple sensor elements to light sources and detectors.Generally, a larger sensor geometric area and a close matching of thesensor element geometric area with photodetector area will providebetter sensitivity.

2. Array Configuration

[0138] The cross-reactive sensor array of the present invention maycomprise either analyte-specific or broadly responsive sensor elements.The number of sensor array elements can be configured for specificsampling applications requirements. Specific sensors for definedanalytical tasks can be chosen from among the many possible sensingelement sites present in the array. Sensor and array configurations maybe modified through the addition of additionalLED-sensor-photodiode-filter channels depending on the requirements of aparticular analyte discrimination task.

[0139] In one preferred embodiment, multiple sensor arrays and arraysubstrates may be deployed in the sampling chamber. Such multiple arraysmay comprise a series of hierarchically organized sensor arrays suchthat the first interaction and sampling of the analyte is with a broadlyresponsive sensor array and, subsequently, the analyte sample isautomatically diverted for additional sniffs, on the basis of analyticalinformation fed back from the computer, to specific second order arraysdesigned to detect and identify the specific type of analyte. Thus, aplurality of sensing arrays may be arranged hierarchically so that everfiner discriminations can take place successively along the pathway.Additionally, the longevity of sensors can be extended by redundantarrays that are protected from exposure until needed; by delivery ofanalytes as short pulses, and by reducing light exposure by rapidlypulsing LEDs. Low light excitation levels can be used if highsensitivity photodetectors such as avalanche photodiodes are employed.Rapid short pulsing of analytes prevents sensing surfaces from everreaching equilibrium.

[0140] For enhanced, smart mode operation, the number of array sensorsused in sampling or detecting an analyte may be modified, in real-timeduring either actual sampling or post-sampling data analysis using“on-the-fly” intelligent feedback control. By way of example, if aspecific sensor is unresponse to a particular analyte sample, thecorresponding sensing channel may be automatically removed fromconsideration by a smart sampling or analysis algorithm providesfeedback control to the microcontroller. In addition, the weighting ofindividual sensors in the analysis and detection algorithm may beadjusted based on the signal contribution of individual sensors. Giventhat individual sensors have different breadths and peaks of response,sensor weighting will vary for different analytes.

[0141] In one preferred embodiment a 32 channel sensor array isemployed. It is anticipated that an array of thirty-two sensor elementsshould have the capability of detecting at least 1000 different analytetypes, as long as the sensors materials employed provide sufficientdiversity in their analyte detection capability and are appropriatelybroad in their spectra of response. While the results presented inExamples 1 through 4 were generated for array sizes ranging from ninesensor elements to thirty-two elements, one skilled in the art mayincrease or decrease both the size of the sensor array and number ofsensing channels, following the teachings disclosed herein, for meetingspecific sensing application requirements.

E. Optical Detection System

[0142] Typically, epi-illuminating optics are employed with conventionaloptical sensing systems. Epi-illuminating optics require relativelycomplex dichroic mirror arrangements for each channel where a differentexcitation and emission wavelength is used. Thus, in theepi-illumination format an excitation filter, a dichroic mirror, and anemission filter are required for each wavelength. The sensing system ofthe present invention employs a trans-illumination configuration whereonly excitation and emission filters are needed. Since theepi-illumination mode typically requires critical optical componentalignment and is sensitive to vibration and movement, thetrans-illumination mode of the present invention is advantageous forrobust, compact, portable sensing devices for field sampling of ambientenvironments.

[0143] A schematic diagram of the optical detection system of thepresent invention is provided in the block diagram of FIG. 3. FIG. 8provides a cross-sectional view of the sampling chamber thatschematically shows the configuration and relative orientation ofindividual LED-photodiodes-optical filters-sensor pairings within thesampling chamber housing. For simplicity, the cross-sectional view inFIG. 8 shows only three sensing channels, comprising threeLED-photodiode-filter-sensor channel pairings. A schematic exploded viewof a nine sensor array configuration is shown in the inset of FIG. 8. Itis important to note that the partial array configurations shown in FIG.8 are merely used to demonstrate, by way of example, the relativeorientation and positioning of the sensors, filters, photodiodes andLEDs in the sampling chamber and are not intended to indicate any;limitation in the size of sensor arrays that may be employed in thepresent invention. The actual sensing device of the present inventionmay employ larger or smaller arrays and any number of sensing channelswith corresponding LED-photodiode-filter-sensor parings. For example, inone preferred embodiment, 32 LED-photodiode-optical filters-sensorchannel parings are employed. The number of sensor array channels may beincreased or decreased depending on specific sampling applications andanalyte discrimination requirements.

1. Array Components Configuration

[0144] The configuration and relative orientation of LEDs, photodiodes,excitation filters and emission filters, sensors and sensor arraysubstrate is shown schematically in FIGS. 13a-b. While an eightsensor-LED-photodiode-filter module is shown in FIGS. 13a by way ofexample, larger and smaller modules and arrays may be constructed basedon specific sampling and detection needs. For example, in one preferredembodiment, a 32 element sensor array may be assembled from four modulesaligned side-by-side with eight sensors in each module. As shown in FIG.13a, a plurality of LEDs are mounted on a nominally 30 mm×30 mm×6 mmblack plexiglass support by drilling two columns of four 3 mm holes in a2×4 array configuration. The LEDs are press fit into the mounting holesand may be readily removed for replacement. A photodiode support withthe same dimensions is used for mounting a plurality of eightphotodiodes in a 2×4 array configuration. Both the LED and photodiodearrays are mounted in columns with pair row spacings of 6 mm center tocenter and interpair spacings of 8 mm center to center. Column spacingfor both the LED array and photodiode array is 15 mm center to center.

[0145] As shown in FIG. 13a, 12.5 mm (½″) diameter excitation filtersare mounted on an approximately 30 mm×30 mm×6 mm excitation filtersupport formed by drilling. four ½″ holes in a black plexiglass supportplate to accommodate the filters in a 2×2 array configuration. Otherfilter assembly configurations, containing a larger or smaller filterarray with larger or smaller filters may be employed in otherembodiments. A similar emission filter support with the same dimensionsas the excitation filter support is fabricated for mounting fouremission filters. The emission filters and excitation filters aremounted to their respective supports with conventional set screws. Theresulting excitation filter support assembly is attached directly to thefront face of the LED support assembly and the emission filter supportassembly is attached directly to the front face of the photodiodesupport assembly with conventional mounting screws.

[0146] A plurality of sensor elements are applied either directly to atransparent sensor array substrate, for example a glass coverslip, ascoatings or droplets. Alternatively, where porous or fibrous sensingelements are employed, these may be taped, glued, or clamped to atransparent sensor array substrate, or suspended over openings orperforations in an array support substrate which may be eithertransparent or opaque. As shown schematically in FIG. 13b, removable,interchangeable sensor array substrates, or array support substrates,are mounted flush with the front face of the emission filter supportusing an substrate support holder. The substrate support holder isformed by gluing a U-shaped substrate support frame and a U-shapedsubstrate support facing to the front fact of the emission filtersupport. The sensor array substrates, or array support substrates, areslidably mounted in a slot or channel formed by the substrate supportframe, support facing and front face of the filter support as shown inFIG. 13b. The substrate support assembly provides for rapid removal andreplacement of the interchangeable array substrates or array supportsubstrates.

[0147] The sensor array may comprise either a single sensor arraymodule, as shown in FIG. 13a, or a plurality of sensor modules alignededge-to-edge to form a multi-module array containing a large number ofsensor elements. The bottom edge of both the LED-excitation filtermodule support assembly and the photodiode-emission filter-sensor modulesupport assembly are secured to a chamber support plate withconventional mounting screws. In this configuration, the excitationfilter side of the LED assembly faces the sensor array side of thephotodiode assembly. The LED and photodiode modules, or plurality ofmodules, are preferably aligned parallel to one another with spacingbetween the two modules adjusted to optimize illumination of the sensorarray elements by the LED array. In one preferred embodiment shown inFIG. 13a, this spacing is approximately 9.5 mm. In one preferredembodiment, a 32 sensor array is formed by mounting four eight sensormodules ton the chamber support plate. Other configurations using largeror smaller sensor modules and a fewer or greater number of modules maybe employed to accommodate smaller or larger arrays by adjusting thesize of the LED, photodiode, filter and sensor supports and chambersupport plate and adjusting the spacing between opposing LED andphotodiode modules to optimize illumination of sensor array elements bythe LED array.

2. Excitation/Emission Filters

[0148] Commercially available, optical bandpass excitation filters forLED light sources and emission filters for photodiode detectors wereobtained from Andover Corp. (Salem, N.H.). While these filters areavailable in ¼ to 1½ inch sizes, ½ inch filters were used in preferredembodiment. By way of example, FIG. 13 shows schematically the relativeorientation, configuration and spacing of excitation and emissionfilters for an embodiment which employs 32 sensors and sensing channels.For simplicity, FIG. 13 shows only one of four eight-sensor modulesemployed in a 32 channel sensor array. In this embodiment, with foursensor modules, 16 Excitation filters are arranged in a 2×8 array with acenter to center distance of 15 mm. With this embodiment, each emissionfilter covers a pair of two adjacent photodiodes having a 6 mm center tocenter spacing. In this particular embodiment, the.32 sensor elements inthe array were aligned with the center of the LED-photodiode pair sightline. Other embodiments are envisioned where each sensor channel has itsown individual excitation and emission filter or where more than twosensor channels share each excitation and emission filter.

[0149] The excitation and emission filters that were utilized forspecific sensor materials in one preferred embodiment are listed below.Note that the filters are designated by center wavelength, followed by“FS”, then the bandpass at 50% amplitude.

[0150] 1. Nile Red:

[0151] excitation—533FS40

[0152] emission—600FS10, 610FS10, 620FS10, 633FS10, 640FS10, 650FS10,660FS10

[0153] 2. Nile Red+Poly(N-vinylpyrrolidone):

[0154] excitation—533FS40

[0155] emission—600FS10

[0156] 3. Nile Red+Poly(ethyl cellulose):

[0157] excitation—533FS40

[0158] emission—61OFS10

[0159] 4. Nile Red+Poly(dimethyl siloxane):

[0160] excitation—533FS10

[0161] emission—633FS10

[0162] 5. Nile Red on Millipore glass filter:

[0163] excitation—533FS40

[0164] emission—650FS10

[0165] 6. Pentiptycene-derived phenylenecthynylene polymer 1:

[0166] excitation—460FS10 // 430FS10

[0167] emission—488FS10, 500FS10 // 470FS10, 510FS10

[0168] 7. 4-(dicyanovinyl)julolidine (DCVJ):

[0169] excitation—460FS10 // 430FS10

[0170] emission—488FS10, 50OFS10 //470FS10, 510FS10

3. Excitation Light Sources/LEDs

[0171] Illumination of sensor elements with excitation light energy maybe accomplished with any appropriate light source. Thus, filtered lightemitting diodes (LEDs), solid state lasers, or incandescent lightsources of the appropriate wavelengths for the dye indicators being usedmay be employed. In a preferred embodiment, each LED light is passedthrough an excitation filter matched to a specific sensor element dyeexcitation wavelength. Where excitation filters are employed, broad band(“white”) LEDs with appropriate wavelength filters may be used.

[0172] Unlike conventional sensors, by providing individually filteredsensing channels, the present invention enables simultaneous sampling atmultiple excitation wavelengths and multiple emission wavelengths withdifferent sensor elements. The present invention uniquely provides forindividual control over the amplitude, duration, and duty cycle ofillumination for each sensing channel in the array. Control over noiseis exerted by feedback. Control over response to ambient light andoptimization of signal detection, including reduction of dye bleaching,is accomplished by switching and modulating LED output and coordinateamplifier detection at various frequencies, ranging from kilohertz tomegahertz. Control over ambient light interference may be achieved byphase locked LED flashing and photodiode detection.

[0173] In the present invention, sensor elements are illuminateddirectly by focussed, light emitting diodes (LEDs) of the correctwavelength for each sensor dye material. Other advantages achieved fromusing LED excitation light sources are low power requirements, cooleroperating temperatures, and high light output over small area.Additionally, by employing LED light sources for each array sensingchannel, each LED channel can be rapidly and independently switchedelectrically without use of a mechanical shutter. The LED channels canbe individually modulated electrically at high rates by feedback fromthe microcontroller. In addition, the LED channels can be individuallyfiltered for presenting different excitation wavelengths in parallel,thereby avoiding serially and mechanically switching filters duringarray measurements.

[0174] For delivering green light with a peak at 530 nm, E903 MegabriteLEDs (Gilway Technical Lamp, Woburn, Mass.) run at maximum current areused. With this LED model, excitation of the dye Nile Red has beenachieved both without excitation filters, using the raw LED output andwith excitation filters with peaks at 532 nm+−10 nm. For blue light witha peak at 430 nm, cat. #25-346 blue LEDs manufactured by Everlight(Hosfelt Electronics, Inc., Steubenville, Ohio) run at maximum currentare used. Excitation of fluorescent detector materials in the blue haveused filters from Andover with a peak at 430 nm+−10 nm.

[0175] The LED's are turned on and off under computer control. Sincethese devices can respond at high speeds, up to megahertz frequencies,they are typically flashed at kilohertz frequencies in order to reducebleaching. Such switching speeds cannot be achieved using mechanicalshutters. The rapid switching capacities of LED's are utilized to flashthem on and off in order to reduce sensor bleaching during dataacquisition. This is achieved by pre-bleaching sensors before samplesniffs and by reducing total light exposure by shortened duty cycleduring sample sniffs. This is accomplished by rapidly flickering the LEDso that light is only on during the time when data are being taken andthen turned off between data points and between trials.

[0176] The electrical circuit controlling the LED's, which are connectedin parallel, is shown in FIG. 5. In this circuit a Radio Shack powerIFR510 MOSFET (Tandy Corp., Fort Worth, Tex.) is controlled by one ofthe input/output lines (see pin 35 of connector J2 from the computer inFIG. 12) under software control.

4. Detectors/Photodiodes

[0177] While a variety of photodetectors such as photomultiplier tubes(PMTs), charge-coupled display device (CCD) detectors, photovoltaicdevices, phototransistors, and photodiodes may be used for detectingsensor response signals, in a preferred embodiment, filtered photodiodedetectors are employed. In another preferred embodiment, highlysensitive avalanche photodiodes may be employed. Photodiode detectorshave distinct advantages compared to conventional CCD camera detectorssince they enable independent control and modulation of individualchannel optical filtering, current/voltage conversion, signalamplification,. and temporal filtering. Other specific advantages arelow power consumption, relatively simple electronic circuitry, highsensitivity, configurability, multiple array formats (e.g. circular,square, or linear arrays), fast high frequency response at megaHertzfrequencies, low noise, wide dynamic range, and use with low frequencycircuits.

[0178] In the sensing device of the present invention, an array offiltered photodiodes is employed where each filtered photodiode iseither aligned with one filtered LED or, alternatively, groups offiltered photodiodes may be illuminated by a single filtered LED. Theindividual photodiodes are each aligned with an individual sensorelement site with an optical emission filter that is appropriate for thespecific dye employed by the individual sensor. Different emissionfilters may be used for each photodiode or, alternatively, one emissionfilter may be shared by multiple photodiodes. Photodiode signal noise iscontrolled by feedback. Additionally, feedback control is exerted. overthe signal sampling duration and time course. Differential signal inputsmay be employed with a separate control sensor and individual samplingsensors. In one preferred embodiment, highly sensitive avalanchephotodiodes may be used to permit lower required LED intensity forsensor of excitation and for reducing detector noise.

[0179] In one embodiment commercially available EG&G VTP 1232photodiodes (EG&G, Inc, Gaithersburg, Md.) and commercial 12.5 mmemission filters (Andover Corp., Salem, N.H.) were used. Specificemission filters used in conjunction with the photodiode detectors arediscussed above.

[0180] While sensors may share the same LED, photodiode andexcitation/emission filters, in alternative embodiments, separate LED,photodiode, sensor, and excitation/emission filters may be employed foreach of sensor element and sensing channel. In one embodiment,Individual sensor elements and sensing channels may employ differentsensing materials, different excitation wavelengths, and/or differentemission wavelengths simultaneously. While the results provided inExamples 1 through 4 were generated for array sizes ranging from ninesensor elements to thirty-two elements, one skilled in the art mayincrease or decrease both the size of the sensor array and number ofsensing channels, following the teachings disclosed herein.

[0181] The changes in fluorescence as a result of the odor interactingwith the sensing material is detected by a photodiode and current tovoltage (I/V) converter (FIG. 9) originally designed by WarnerInstruments (Hamden, Conn.) and now commercially available from RedShirt Imaging Inc. (Fairfield, Conn.). There is one I/V converter (FIG.9) and amplifier/filter (FIG. 10) for each detector channel. The uniquefeature of this converter/amplifier configuration is that when the LEDsare activated prior to sample delivery, the background fluorescencesignal produced by the sensor elements may be offset by resetting theamplifiers to a baseline value so that a full range of high gainamplification may be used to observe small changes in the signalsgenerated by analytes during sampling. In addition, the innovativeamplifier board has the option for software control to be exerted overthe gain and the filter time constants for all the channels (seeconnector J2 in FIG. 12). Thus, in addition to being able to manipulatethe onset and duration of the illumination and of the sniff as describedabove, the time constants and gain of the amplifiers can also becontrolled in real time during data acquisition. These hardware featuresoffer distinct advantages for optimizing the response of the sensingdevice for detection, discrimination and identification of analytes orodors of interest.

F. Electronics—Analytical and Control Circuitry 1. Analytical Circuits

[0182] Generally, the sensing system of the present invention analyzesspatial-temporal patterns of data output (see FIG. 20) from sensorarrays in order to characterize and identify the delivered sample or itsanalyte components. Useable information from the sensing array isgenerated from the pattern of sensor response activity generated by allsensor elements over time and is evaluated using statistical measuressuch as information theory. Pattern recognition algorithms includingtemplate comparison, neural networks, principal components analysis,etc. may be implemented either in conventional digital CPUs, in neuronalnetwork simulator chips, or in analogue neuronal network computers.Additionally, algorithms based on biologically based neuronalconnections from the olfactory system and other neuronal circuits in thebrain may be employed. The innovative analytical circuits of the presentsensing device provide the requisite hardware support for the detection,discrimination and identification capability of the sensing system.

[0183] In one preferred embodiment The circuits comprise current tovoltage converters for each photodiode (FIG. 9) and photodiodeamplification (FIG. 10) with variable gain controlled both manually andby feedback from the computer (FIG. 12). Amplifiers are reset after LEDsare switched on to start the data conversion process at zero volts, asset by a voltage divider on the amplifier output. This permits bothpositive and negative differences in fluorescence to be recorded. Timeconstants of each amplifier channel are controlled both manually and byfeedback from the computer (FIG. 12). 12 bit, or alternatively, 16 or 24bit, analogue to digital (A/D) conversion of signals from each sensingphotodiode is provided. Multiplexing of multiple sensing channels isprovided via the microcontroller computer (FIG. 12).

[0184]FIG. 9 shows a standard current to voltage (I/V) converter usingan Analog Devices AD548 operational amplifier with a choice of feedbackresistors of 1 or 0.5 megohms controlled by a software switched gate(2N4119) to control the frequency response and noise properties of theIN board. This circuit converts current changes in the photodiodesresulting from different levels of light exposure to voltage changes thtare fed to the amplifier circuit shown in FIG. 10.

[0185] The standard amplifier circuit in FIG. 10 consists of operationalamplifier transistors (AD548) in circuits which provide 1) a choice oftime constants (DC, 500 ms, 100 ms); 2) resetable baseline; 3) and achoice of gains (1x, 50x, 200x, 1kx). All of these attributes are undersoftware control via input/output (I/O) control lines from the computervia the 2N4118 gates. The filter section of the amplifier is run by aclock line from an oscillator on the computer control and amplifiercontrol board shown in FIG. 12.

[0186]FIG. 5 shows the circuits to control illumination of the LEDs. Thegate of the MOSFET, IFR510, is controlled by one of the computer I/Olines under software to turn the LEDs on and off at the time designatedby the program. The LM317 is an adjustable voltage regulator thatdetermines the voltage delivered to the LED bank and thereforedetermines the intensity of the LEDs. The LM317 is controlled by anoutput digital to analogue line from the computer under softwarecontrol.

[0187]FIG. 11 shows how the output lines from the amplifier channels areconnected to the appropriate input lines of the analogue to digitalconverters in the microcontroller computer. There are no activeelectronic components here, only wired connections.

[0188]FIG. 12 shows how the I/O lines from connector J2 of the SmartLCDcomputer control the various function of the device and how power isprovided to the preamplifier and amplifier boards. Regulated + and −12v. and regulated + and −5 v come in through the main power connector inthe upper left of the figure. These voltages are distributedappropriately to the power connectors for the preamp and amplifierboards. The J2 connector provides I/O line control for the MOSFET thatcontrols the LEDs (as described for FIG. 5) through the ‘LED/fan’control connector. The inhale and exhale valves are also controlled byI/O lines going to this connector. The remaining I/O lines from J2control the gates (as described for FIG. 10) that control the timeconstants, the reset, and the gains on the amplifier board. The 555timer generates the appropriate clock signal (˜4kHz) for the filters onthe amplifier board. The Siliconix DG442 is simply an intermediatesoftware controlled switch that interfaces the I/O lines with the resetline on the amplifier board.

[0189]FIG. 12 shows the interface circuit that allows themircocontroller computer to control the LED's, the fan valves(inhalation and exhalation), the amplifier reset, and the amplifier gainand time constants from connector J2. As shown in FIG. 4, in oneembodiment, 32 channels are digitized to 12 bits after going through avoltage divider such that, after the light is turned on and theamplifiers reset, fluorescence differences in both positive and negativedirections can be detected. The number of sensing channels may beincreased or decreased by replicating or removing the individual channelcircuits shown schematically in FIGS. 4, 5, 9, 10, 11 and 12.

[0190] The device is controlled by a TERN Smart LCD microcontroller(Tern,lnc., Davis Calif.) computer running at 40 MHz with 512 K RAM, 66channels of 12 bit A/D, and programmed in ‘C’ programming language. Inalternative embodiments, a faster computer may be employed (e.g.PIII-730 with 1 GB RAM) to yield shorter detection times.

[0191] All electronic parts and circuit components are conventionallyknown and readily available at standard electronic suppliers such asRadio Shack or DigiKey. The I/V (FIG. 9) and amplifier boards (FIG. 10)were designed and built by Warner Instruments (Hamden, Conn.) but aremade from conventional, commercially available components fromelectronic suppliers.

[0192] For the standard electronic parts employed in the describedembodiments there are many interchangeable substitutes which are knownand used in the electronics art. One skilled in the art could substitutemany equivalent programmable microcomputer controllers as long as theyprovide a minimum of at least 12 bit or greater analogue to digitalconverters, an easy input device (e.g. keypad) and a simple outputdevice (e.g. LCD display).

III. Sensing Method A. Overview

[0193] An innovative feature of the present invention is the use oftemporal control over stimulus presentation and the examination of theresulting changes in sensor output over time. Unlike conventionaldesigns, with the present invention analyte presentation to the sensingsites is carried out by negative pressure ‘sniffing’, rather than byconventional positive pressure pulsing which requires samples to beenclosed in confined containers. An additional innovative feature of thepresent invention is that sniffing parameters can be electronicallymodulated by feedback from via computer control and flow rate, sniffduration, and temporal profile can be adjusted and modulated forspecific sampling environments and target analytes to detect ambientodors drawn into the sensing chamber. Sampling modulations can becarried out in real time so that subsequent sniffs can be modified bythe preceding ones. With the smart sampling mode capability of thepresent invention, a computer turns the sniff on and off and canmodulate and control sniff parameters during a sampling.

B. Training Runs

[0194]FIGS. 15 and 21 provide schematic flowcharts of typical trainingmethods employed with the sensing device of the present invention.Further details of smart mode training are discussed in later sectionsand details of one training embodiment are described in Example 3.

[0195] Target samples of known analytes (odors), either pure compoundsor complex mixtures, are required for training the sensing device andidentifying unknown analytes in sampled fluids. Training samples aretypically provided in small, disposable, plastic screw top jars whichare vapor tight. A small paper cup insert may be employed with thesample jars as a disposable liner to facilitate cleaning. For typicaltarget training samples, two cotton balls are placed in paper cup thatis positioned inside the sample jar and analyte, odor-generatingmaterial is typically added either as a liquid or solid (e.g. camphor,chocolate, cloves, and orange peels). The cotton provides a high surfacearea for promoting evaporation and prevents unrestrained liquid samplesfrom spilling.

[0196] For all training runs, initially a clean air test sniff is firsttaken by initiating the automated sampling sequence which provides forturning on the LEDs, taking digitized data from the photodiodes,measuring background fluorescence and storing this in memory, turning onthe sniff pump, turning off the pump, terminating data acquisition, andturning off the LEDs. The device is then trained for target analytes byplacing the target analyte sample container into position and initiatingthe automated sampling sequence. The sequence of sampling and dataacquisition events for target analytes is the same as for the airbaseline sample. This training sequence is repeated for each targetanalyte of interest and response data are stored in the microcontrollercomputer RAM memory module.

C. Sampling Runs

[0197]FIGS. 16 and 22 provide schematic flowcharts of typical samplingprocedures employed with the sensing device of the present invention.Further details of smart mode sampling are discussed in later sectionsand details of one sampling method embodiment are described in Example3.

[0198] The sequence of steps for sampling analyte-containing fluids aresimilar to the training runs described above. A typical samplingsequence is shown schematically in FIG. 16 and discussed in more detailin later sections. The entire sampling sequence is controlled by anmicrocontroller computer embedded in the sensing device. The sampletiming sequence is, shown in FIG. 14. A typical sampling run sequence isas follows:

[0199] 1. Set inhalation and exhalation fan valves in partial exhalemode to prevent uncontrolled diffusion of ambient analytes into samplechamber.

[0200] 2. LED's are turned on for 100 ms.

[0201] 3. Amplifier baselines are reset while LED's are on (this zeroesout the background fluorescence).

[0202] 4. LED's turned off

[0203] 5. Wait 150 ms

[0204] 6. Steps 1-3 repeated 5 times to insure amplifier reset isstable.

[0205] 7. Analyte response run begins

[0206] 8. Turn on LED's for 100 ms

[0207] 9. Take an analog data point from each sensor, convert to digitalvalue with 12 (0-4095) bit accuracy, place digital value in memory

[0208] 10. Turn LED's off

[0209] 11. Wait 150 ms

[0210] 12. Repeat steps 8-11 one time (this is before analytepresentation)

[0211] 13. Switch inhalation valve on and exhalation valve off (see FIG.6a)

[0212] 14. Repeat steps 8-11 four times (for 1 sec analyte pulse)

[0213] 15. Switch inhalation valve off and exhalation valve on (see FIG.6b)

[0214] 16. Take 4 more data points (repeating steps 8-11)

[0215] 17. Analyte presentation and data acquisition phases are complete

[0216] 18. Evaluation circuits and algorithms characterizespatio-temporal response data of the array either via patternrecognition algorithms, template matching, a neural network, statisticalanalysis, or other analytical methods for analyte identification

[0217] 19. Results may be displayed on screen, spoken by voicesynthesis, or plotted as a three-dimensional response surface offluorescence changes from each sensor at each time point duringsampling. If sensing device is on robotic vehicle, results are processedfor feedback control and decision is made to stay on course or executean appropriate maneuver

[0218] Optionally, where multiple samples or complex mixtures containingmultiple analytes are being sampled, the above sampling steps may berepeated following initiation of the next analyte application with datasampling and acquisition modifications based on intelligent feedback viasmart algorithms. Thus, real-time, on-the-fly feedback can dynamicallymodulate either LED, photodiode, or sniffing hardware settings, or,alternatively, analyte sampling parameters such as, sample duration,rise time, relaxation time, delay from previous sniff, amplifier gainand time constants may be modified. These modifications may be imposedon the next data acquisition within the same sampling trial untildetection and identification of the analyte occurs.

D. Data Acquisition

[0219]FIG. 14 shows the timing events for a typical data acquisition runduring sampling. The smart mode features of the present inventionprovide for feedback to be applied between or within single sniffs. Thetop four traces in FIG. 14 represent control signals; the bottom threetraces represent signals from three different sensor channels,illustrating different responses to the same analyte. Upward deflectionsin the “LED” trace indicate when the LEDs are turned on. Upwarddeflections in the “Amp Reset” trace indicate control pulses sent to theamplifier to reset the baseline to zero. Thus, the first upwarddeflection for each sensor is the response to illumination; resettingthe amp brings this level to zero. When the LEDs turn off, the sensorsignal goes to a negative value (only two amplifier resets are shownhere for simplicity—we typically reset five times). The upwarddeflections in the “ADC” (analog-digital conversion) trace indicate whendata points are collected, digitized, and stored in computer memory.These data points are represented by dots on the sensor traces. Theupward deflection in the “Sniff” trace indicates when inhalation occursand analytes reach the sensors. “Sensor 1” shows a slowly respondingsensor that shows an increasing fluorescent signal to a saturating levelwith analyte, “Sensor 2” shows a rapidly responding sensor that quicklysaturates, and “Sensor 3” shows a slowly responding sensor that shows adecreasing fluorescent signal, but does not saturate.

[0220] As shown in FIG. 14, LEDs are pulsed (LED trace) to reduceproblems with sensor photobleaching. The amplifier reset (Amp Resettrace) is critical during sampling to providing. zero offset so thatsmall response signals can still be detected where there is highbackground fluorescence. Analog/Digital conversion (ADC trace) occurseach time data is collected from sensor element channels in the array.While each sensor element/detector combination within the array willhave temporal response pattern, only response timings for three sensorchannels are shown in FIG. 14. The dots placed on the sensor responsesignal schematic indicate times at which data points are collected Thethree schematic sensor signals represent simple examples of possibleresponse types that would benefit from feedback control. Sensor 1 showsa baseline signal condition. Sensor 2 shows a rapidly responding sensorsignal where the signal saturates and is clipped with loss of signalinformation. With feedback modulation of this sensor during sampling,subsequent runs may be set to lower amp gain to prevent signalsaturation and data acquisition speed may be increased to yield moredata in the rising portion of the sensor signal. Sensor 3 shows a slowlyresponding sensor signal. With feedback modulation of this sensor duringsampling, data acquisition speed may be reduced in subsequent runs toallow the response signal to develop more fully, yielding a largersignal.

[0221] The steps taken in training the sensor and testing for analytes,including data analysis and matching, are shown in the flow charts ofFIGS. 15 and 16 and the timing diagram of FIG. 14. Both FIGS. 15 and 16represent the steps taken in software. The “Acquire” steps are thepoints where the program controls the hardware to take data as shown inthe timing diagram of FIG. 14.

[0222] The software program explicitly controls the pre-bleaching phase,the duration for which the LED′ illuminate the sensors, the onset ofdata acquisition, the application of the analyte, the duration ofanalyte presentation, the cessation of analyte application, the durationof the integration time for each data point, the number of time points,and the interval between time points. All of these parameters can bemodulated either by direct operator intervention or, alternatively, byprogramming the microprocessor with smart algorithms that modify thesampling, data acquisition, or analysis steps through real-time feedbackcontrol.

E. Data Analysis

[0223] The data are filtered, smoothed, statistically evaluated,compared with libraries of stored templates for odor identification,.and/or operated on by any of the algorithms discussed below. The dataare typically stored in memory as an array of numbers representing thetemporal changes in fluorescence in each sensing channel.

1. Detection Methods and Algorithms A. Evaluation of Synchrony, ResponseSignals and Noise Characteristics

[0224] To improve the detection and discrimination capability of thesensor of the present invention, additional algorithms may be employedto evaluate “synchrony” of response data across different sensorelements to identify small response signals and reject noise. Evaluationof “synchrony” refers to analyzing how many signals coming fromidentical. sensors are similar in the context of when they occur duringthe sniff cycle. The field that encompasses analytical algorithms isvery large and many analytical approaches are available. Due to theinnovative features of the present invention, such as the use ofmultiple detector channels with different wavelengths, use of single ormulti-pulsed analyte presentation, and the ability to acquire data fromsensor elements in parallel rather than serially, the design of thepresent invention enables consideration of a number of alternativealgorithms beyond those that are conventionally used in artificialnoses. This is what is meant by the term “synchrony”. Additionally, inpreferred embodiments algorithms which are based on biological circuitsmay be employed [see J. White, et al., Biol. Cybern. 78:245-251(1998);J.White, et al., Anal.Chem. 68(13):2191-2202 (1996); and S. R. Johnson,et al.,Anal.Chem. 69(22):4641-4648(1997), which publications areincorporated herein by this reference]. The device of the presentinvention may employ synchronously occurring signals in some embodimentssince sensor response data are acquired simultaneously in parallel.

B. Detection Algorithms

[0225] The degree to which the response matrix of a test substancecorresponds to one of the target analyte library matrices stored duringthe sensor training phase can be evaluated in a number of ways.

[0226] In one preferred embodiment, a sum of the squared differencesbetween each value in the test matrix and the training matrix aregenerated. These sums may be evaluated by subtracting the test matrixfrom all of the stored matrices. The smallest sum may be used toidentify the best target analyte match. This method was used for thespecific embodiments described in Examples 1-4.

[0227] In an alternative preferred embodiment, a supervised, for exampleback propagation, neural network approach may be employed. Examples ofthese methods are provided in J. White, et al. “Rapid AnalyteRecognition In A Device Based On Optical Sensors And The OlfactorySystem”, Anal. Chem. 68(13):2191-2202 (1996) and S. R. Johnson, et al.,“Identification Of Multiple Analytes Using An Optical Sensor Array AndPattern Recognition Neural Networks”, Anal. Chem. 69(22):4641-4648(1997).

[0228] In another preferred embodiment, analytical circuits based on theolfactory system may be employed as disclosed by J. White, et al., “AnOlfactory Neuronal Network For Vapor Recognition In An Artificial Nose”,Biol. Cybern. 78:245-251(1998).

[0229] In another preferred embodiment, unsupervised neural networks maybe used. Principle component analysis and multidimensional scaling are,in effect, unsupervised statistical methods for reducing dimensionality.Generally, unsupervised neural networks organize high dimensional inputdata into lower dimensional representations. For example, assuming oneembodiment of the present device with 32 sensors and 20 time points, atotal of 640 data points may be collected. In this embodiment, eachanalyte presentation can thus be thought of as a point in 640-dimensionspace, which, while difficult to visualize, may be mathematicallymanipulated. By averaging across sensors and time, the datadimensionality may be reduced, but typically data dimensionality aboveabout four dimensions is rather difficult to visualize.

[0230] Self-organizing maps (SOMs) are unsupervised neural networks thataccomplish similar things. Such SOM methods are attractive forrepresenting artificial olfactory system data because they give avisualization of “odor space”. In other words, a map of relationshipsamong various analytes can be produced during training; then duringtesting, the location of a test analyte on the ‘map’ indicates therelationship of the analyte with respect to this ‘space’. Thus, SOMs mayhelp to visualize relationships among analytes, rather than simplyindicating the similarity of an unknown analyte to a target. Examples ofSOM approaches which may be particularly useful for analyte detection,discrimination and identification are disclosed by T. Kohonen. et al.,“SOM-PAK: The Self-Organizing Map Program Package”, Report A31, HelsinkiUniversity of Technology, Laboratory of Computer and InformationScience, Espoo, Finland (1996) and T. Kohonen, Self-Organizing Maps,Series in Information Sciences, Vol. 30, 2^(nd) ed., Springer-Verlag,Heidelberg (1997), which publications are incorporated herein by thisreference.

C. Sampling and Detection Parameter Modulation

[0231] Upon evaluation of the response matrices generated by thestandards used for training, modifications in sniffing parameters, gainsettings, and/or filter settings may be made for actual sampling ofambient fluids. In a standard operating mode, these modifications may bemade through interventions of an operator who manually changes samplingand data acquisition parameters through the programmable microcontrolleror by keyboard entry. In alternative smart operating modes described insubsequent sections, these modifications may be made automatically,on-the-fly by smart sampling and detection algorithms that directmircocontroller operations.

[0232] Whether and how much such modification improve sensingperformance may be evaluated by examining sensor responses afterfeedback and determining, by some predetermined or analytically-derivedcriterion, whether current sample data are better or worse than dataobtained on a previous run. Modifications may also consist ofdifferentially weighting the influence of sensors, so that those sensorsthat give the best signals have a greater impact in the recognitionalgorithms. This can be done in a number of ways, such as eliminatingsensors that give little or no signal so as to reduce noise, normalizingthe remaining signals to some standard value in order to use the maximumrange available, or changing analyte sampling and stimulus acquisitionparadigm to optimize sniff sampling parameters.

D. Smart Mode Operation

[0233] Example 3 provides one example of an embodiment of the smart modesampling capability of the present invention where the number andduration of analyte samples taken during a sample session are controlledby way of real-time feedback and control loops for improving detection,discrimination and identification of analytes. In other embodiments,alternative smart mode parameters and device sampling configurations maybe manually or automatically selected during training and sampling viadevice menu options. Smart mode sampling configurations may be usedalone or in a variety of combinations and permutations. In oneanticipated embodiment, an automated training algorithm may be employedto optimize parameter selection and sampling configuration in order toprovide the best detection and discrimination capability for specificanalytes of interest. Specific examples of alternative smart modesampling options and parameter configurations are described below.

1. Sampling Parameters

[0234] A. Sniff parameters.

[0235] i) Sniff duration. This parameter variation is discussed inExample 3 where significant improvements in detection accuracy arerealized.

[0236] ii) Number of sniffs. In the simplest implementation, signalsacross multiple sniffs may be averaged to improve signal-to-noise.However, different sensors exhibit different long-term responses tomultiple sniffs (providing either increasing signal, decreasing signal,or constant signal over a series of sniffs). Monitoring these changesover sniffs (rather than simply averaging the signals) could provideadditional information for analyte discrimination.

[0237] iii) Sniff dynamics (rise time, fall time). The rate and extentof sample chamber valves opening and closing may be controlled to modifysampling (sniff) dynamics. Changing the sniff dynamics may enhancedifferences in the rising and falling phases of the sensor response.

[0238] iv) Sniff velocity. In one anticipated embodiment, adigital-to-analog line may be used to control a transistor that couldchange the voltage supplied to the sniff fan and alter fan velocity.Changing sniff velocity, in conjunction with changes in sniff duration,may provide optimized exposure of the sensors to particular analytes.

[0239] v) Exhalation velocity. As with changing sniff velocity, a changein exhalation velocity would alter the rate at which analyte is purgedfrom the sensors and the dynamic sensor response may then be monitoredin subsequent sniffs for improved analyte discrimination.

[0240] B. LED intensity.

[0241] While higher LED intensity leads to more rapid photo-bleachingand sensor degradation, it also tends to yield larger sensor responsesignals during analyte exposure. In one smart mode embodiment, normalsampling would be made at lower LED intensity and, where small responsesignals are present, LED intensity may be increased incrementally untilreliable response signals are produced for analyte detection. This smartmode would tend to extend sensor lifetime by operating at minimum LEDintensity to reduce photobleaching.

[0242] C. LED wavelength.

[0243] The excitation wavelength of the LED may be modulated. LEDs arecommercially available that produce three separate wavelengths. Thewavelength of conventional LEDs may be modulated by changing appliedvoltage and flicker frequency. The capability for changing LEDwavelength may permit the device to optimally excite the sensors and tochange that excitation over sniffs to improve discrimination.

[0244] D. Amplifier gain settings. Under typical sampling conditions,the highest gain settings are employed. Under such a condition, someanalytes produce sensor signals that saturate the amplifier. Byproviding for adjustment of gain settings during smart mode sampling, ifan amplifier channel saturates, an additional sniff at a lower gainsetting Would provide more accurate time course and amplitudeinformation.

[0245] E. Amplifier temporal filter settings. In general, changingtemporal filter settings may not be entirely straight-forward sincesensor LEDs are typically flashed during sampling to reduce lightexposure. As shown in FIG. 14, data acquisition and A/D conversion areclosely correlated with LED pulse timing. However, since some detectionenhancement may be achieved by modifying the timing of data acquisitionduring an LED pulse for improved signal discrimination for specificanalytes, modulation of this parameter may improve detection andidentification of certain analytes.

[0246] F) Gain and temporal filter settings for individual channels.While one current embodiment of the amplifier electronics allowmanipulation of gain and filter settings globally (i.e. gain and filterchanges apply to all channels simultaneously), in alternative sensorembodiments, individual sensor channels may also be manipulated forsmart mode sampling and detection.

[0247] Smart mode training and sampling procedures using these and otherparameter variations are discussed in greater detail below.

[0248] 2. Smart Mode Training

[0249]FIG. 15 provides a schematic flowchart for smart mode trainingprocedures. Smart mode training is divided into two main sections:first, the parameters defining the “primary” sniff are determined,followed by a determination of parameters for any “secondary” sniff(s)that may be necessary. The constraints for the two sets of parametersare different: The primary sniffs are applied at regular intervals overlong periods of time and should have minimum impact on sensor lifetimesince they expose the sensors to as little light as possible to reducephotobleaching and to as little analyte as possible to prolong sensorlifetime and shorten recovery time. Secondary sniffs are intended togenerate signals that allow better discrimination to take place.

A. Photobleaching and Bleach Runs

[0250] Exposing a fluorescent sensor to excitation light producesphotobleaching, decreasing the fluorescent output of the sensor. Thisfluorescence recovers over time after the excitation light is turnedoff. When sensors are exposed to excitation light during acquisition ofresponse data at variable intervals, there appears to be morevariability in sensor response. Preferably, response data are acquiredat regular intervals within 15 second periods. Sensor bleach runsestablish this regular interval before data are actually acquired. Thebleach runs are repeated until the signals from the sensors stabilize.

[0251] Bleach runs are acquired without sniffing or taking a sample. Theresponse matrices from these runs are compared to the previous run bycalculating the sum of squares (SS) difference for all data points. Forthe first run, the comparison is to a matrix of zeroes. If the SSdifference is stable, where successive SS differences change little,training target sampling is initiated. If the SS difference is unstable,an 15 second inter-run delay time is used and then the bleach run isrepeated. While the operator may evaluate the SS difference stabilityvisually, this process may be automated by setting a criterion whichprovides for minimum changes in successive SS differences; when thatcriterion is reached, the program continues and training target samplingis initiated.

B. Establish Primary Parameters

[0252] Device parameters are initialized to settings that should givediscriminating signals upon analyte exposure. For example, the LEDs areturned up to the highest intensity by sending the highest voltagepossible out the D/A line (FIG. 3) to the LED controller (FIG. 5) and along sniff at high flow is acquired by sending a voltage signal throughthe D/A control line (FIG. 3) through an LM317 circuit to control theinhale servomotor and fan and shown in FIGS. 3 and 6a. This section ofthe program finds the minimum values for these parameters that leads todiscrimination of analyte signals from air. In the flow chart shown inFIG. 15, the rectangles with rounded corners represent subroutines ofseveral steps that are described below. The “criterion” referred to hereis initially determined through experimentation with a particular set ofsensors and can be subsequently incorporated into the programmablemicrocomputer for automatic control.

[0253] 1. First, sensors that do not respond to any of the analytes arefound. Data from all analytes and air are acquired. For each sensor, theSS difference between air and each analyte is calculated. If a sensordoes not produce a SS difference value above criterion for any of theanalytes in the training set, that sensor is removed from considerationfor subsequent training and testing.

[0254] 2. Second, the lowest permissible sniff flow is determined:

[0255] a) Take single sniffs of all analytes and air.

[0256] b) Calculate SS differences between response matrices of eachanalyte and air

[0257] c) If SS difference values are all above a criterion, reducesniff flow velocity by 10% (i.e., reduce voltage of D/A by 10%) andrepeat from step 1, otherwise increase flow velocity by 10% (unless flowis already maximal) and stop.

[0258] d) All data are saved to flash (non-volatile) memory for possiblelater use.

[0259] 3. Third, a similar procedure is used to determine the dimmestLED setting:

[0260] a) Take single sniffs of all analytes and air.

[0261] b) Calculate SS differences between response matrices of eachanalyte and air

[0262] c) If SS difference values are all above a criterion, reduce LEDintensity by 10% (i.e., reduce voltage of D/A by 10%) and repeat fromstep 1, otherwise, increase LED intensity by 10% (unless LED intensityis already maximal) and stop.

[0263] d) All data are saved to Flash Memory for potential use later.

[0264] e) Because the level of excitation light is likely reduced by thepreceding steps, another set of bleach runs is then taken.

[0265]4. Fourth, the shortest sniff is determined:

[0266] a) Take single sniffs of all analytes and air.

[0267] b) Calculate SS differences between response matrices of eachanalyte and air

[0268] b) If SS difference values are all above a criterion, reducesniff duration by half (i.e., open sniff valve for half the time) andrepeat from step 1, else double the sniff duration (unless sniffduration is already maximal) and stop.

[0269] c) All data are saved to Flash Memory for possible later use.

[0270] 5. Fifth, the fewest time points to collect is determined. Startwith the short sniff data stored in the previous step (it is notnecessary to collect new data here):

[0271] a) Start by considering data up to the time point just after thesniff begins.

[0272] b) Calculate SS differences between response matrices of eachanalyte and air

[0273] c) If SS difference values are all above a criterion, stop. Elseconsider 1 additional time point (unless the number of time points isalready maximal) and repeat from step b.

[0274] d) Because the number of time points to collect is likely reducedby the preceding steps, another set of bleach runs is taken.

[0275] The result of the “Establish Primary Parameters” section is nowthe lowest flow, dimmest LEDs, shortest sniff, and fewest time pointsnecessary to discriminate analyte signals from air.

C. Establish Secondary Parameters

[0276] The goal of this section is to determine the parameters of one ormore subsequent sniffs, if necessary, that will improve discriminationof analytes that are not discriminating based on the primary sniffalone. The parameter adjustments occur only for the analytes that aredifficult to discriminate. The “criterion” referred to here isdetermined through experimentation with the particular set of sensorsused. It may be different from the criterion used in the primaryparameters section above.

[0277] Step 1. Data from all analytes and air are acquired. If this isthe first time through this step, only primary sniffs are defined andacquired. These data are saved as the primary sniff targets. The SSdifferences between each pair of response matrices is calculated Thisincludes responses to secondary sniffs, if defined. If all SS differencevalues are above a criterion, all targets are deemed to be capable ofdiscrimination. Names are assigned to the targets and the system isready for testing (FIG. 16). Otherwise, go to step 2. All of thefollowing steps are applied only to those analytes that fail to meet thecriterion of step 1.

[0278] Step 2. If the number of sniffs for the “difficult” targetanalytes has reached a user-determined maximum, this value will probablybe on the order of 3 or so sniffs, warn the user about the difficulttargets. Assign names to the targets and go to testing.

[0279] Step 3. Increment the sniff number by 1.

[0280] Each parameter block attempts to optimize the stated parameterfor each of “difficult” targets. The parameter blocks may be ordered asshown so that the first five parameter modulations do not increase theamount of excitation light exposure.

[0281] 1. Parameter #1—Difficulty in discrimination may be due tosaturation of the amplifier channel. This is apparent if the signal fromany amplifier channel reaches a value of approx. 2000 or −2000 and staysat that level for 2 or more time points. The Yale amplifier has gains of1000×, 200×, 50×, and 1×. If saturation occurs, follow the followingsteps:

[0282] a) Decrease the amplifier gain one step and acquire data from thedifficult targets.

[0283] b) If the SS difference between the difficult targets is nowabove criterion, retain this gain setting for these difficult targetsand go to step 1. If the amp gain is at minimum (i.e., none of the loweramp gains improved discrimination), go to step c. Otherwise, repeat fromstep a.

[0284] c) If any of the gain settings produced some improvement, retainthis setting. Otherwise, reset parameter to original value and go tonext parameter block.

[0285] 2. Parameter #2—Since data from longer sniffs may have beenacquired in the “Establish Primary Parameters” section, investigatethose stored data for improved discrimination. If the SS differencebetween the difficult targets for any of the longer sniffs is abovecriterion, retain the best setting and go to step 1. Else, go to thenext parameter block. If some improvement was made (but still belowcriterion), retain the best setting. Otherwise, reset parameter tooriginal value.

[0286] 3. Parameter #3—Since data from higher sniff velocities may havebeen acquired in the “Establish Primary Parameters” section, investigatethose stored data for improved discrimination. If the SS differencebetween the difficult targets for any of the higher sniff velocities isabove criterion, retain the best setting and go to step 1. Else, go tothe next parameter block. If some improvement was made (but still belowcriterion), retain the best setting. Otherwise, reset parameter tooriginal value.

[0287] 4. Parameter #4—For a sniff, the valves are normally opened andclosed abruptly (i.e., the PWM signal to the servo changes from oneposition to the other instantly). For some analytes and some sensors,opening and/or closing the valves more slowly may help producediscriminating signals. To open/close the valves slowly, the PWM signalto the servos will be changed in smaller steps over time. In otherwords, instead of opening the valve fully at a particular time point,open the valve in two steps over two time points by opening the valvehalf way for the first time point, then fully the next. For an evenslower opening, use three steps: open 1/3 at one time point, 2/3 thenext, and fully the next. A maximum of 5 steps will likely besufficient.

[0288] a) Slow sniff on rate by increasing the number of opening stepsby 1; acquire data from the difficult targets.

[0289] b) If the SS difference between the difficult targets is nowabove criterion, retain this sniff setting for these difficult targetsand go to step 1. If the number of sniff steps is at maximum (i.e., noneof the fewer steps improved discrimination), go to step c. Otherwise,repeat from step a.

[0290] c) Reset number of steps to original value.

[0291] d) Slow sniff off rate by increasing the number of closing stepsby 1; acquire data from the difficult targets.

[0292] e) If the SS difference between the difficult targets is nowabove criterion, retain this sniff setting for these difficult targetsand go to step 1. If the number of sniff steps is at maximum (i.e., noneof the fewer steps improved discrimination), go to step f. Otherwise,repeat from step d.

[0293] f) If any of the sniff on or off settings produced someimprovement, retain the best setting. Otherwise, reset parameters tooriginal values and go to next parameter block.

[0294] 5. Parameter #5—The amplifier filters are normally set at DC—nohigh-pass filtering at all. Adding high-pass filtering may help toaccentuate the rising or falling phases of the sensor signal, leading toimproved discrimination. The filter settings available on the Yaleamplifier have time constants of 500 ms, 100 ms, and 300 ms (increasingthe high-pass cut-off frequency). These values are set using the digitaloutput lines from the Tern computer (FIG. 3).

[0295] a) Increase the amplifier high-pass cut-off one step and acquiredata from the difficult targets.

[0296] b) If the SS difference between the difficult targets is nowabove criterion, retain this filter setting for these difficult targetsand go to step 1. If the filter cut-off is at maximum (i.e., none of thelower filter settings improved discrimination), go to step c. Otherwise,repeat from step a.

[0297] c) If any of the filter settings produced some improvement,retain the best setting. Otherwise, reset parameter to original valueand go to next parameter block.

[0298] 6. Parameter #6—Since data from brighter LEDs may have beenacquired in the “Establish Primary Parameters” section, investigatethose stored data for improved discrimination. If the SS differencebetween the difficult targets for any of the brighter LED settings isabove criterion, go to step 1. Otherwise, go to the next parameterblock. If some improvement was made, but it is below the criterion,retain the best setting. Otherwise, reset parameter to original value.

[0299] 7. Parameter #7—Since data from more data points may have beenacquired in the “Establish Primary Parameters” section, investigatethose stored data for improved discrimination. If the SS differencebetween the difficult targets for any of the increased data points isabove criterion, go to step 1. Otherwise, go to the next parameterblock. If some improvement was made, but it is below the criterion,retain the best setting. Otherwise, reset parameter to original value.

[0300] 8. Parameter #8—It is possible that changing exhale velocitybetween sniffs may improve signals for the second sniff. This parameterblock is placed last in order to attempt to add to improvements producedby previous parameter blocks that are still below criterion.

[0301] a) Decrease exhale velocity by 10% (i.e., decrease voltage toexhale fan via D/A lines and LM317 voltage controller) and acquire datafrom the difficult targets.

[0302] b) If the SS difference between the difficult targets is nowabove criterion, retain this velocity setting for these difficulttargets and go to step 1. If the velocity is at minimum (i.e., none ofthe lower velocities improved discrimination), go to step c. Otherwise,repeat from step a.

[0303] c) Reset velocity to original value.

[0304] d) Increase exhale velocity by 10% and acquire data from thedifficult targets.

[0305] e) If the SS difference between the difficult targets is nowabove criterion, retain this velocity setting for these difficulttargets and go to step 1. If the velocity is at maximum (i.e., none ofthe higher velocities improved discrimination), go to step f. Otherwise,repeat from step d.

[0306] f) If any of the velocity settings produced some improvement,retain the best setting. Otherwise, reset parameter to original value.If the program reaches this point without reaching criterion, then noneof the parameter changes improved discrimination. Warn the user aboutthe difficult targets, assign names to the targets, then go to testing.

D. Smart Nose Testing

[0307]FIG. 16 provides a schematic flowchart for smart mode testingprocedures. Smart Nose testing a single analyte can occur in two stages.First, a primary sniff is taken and, if the primary sniff produces agood match to a target, that match is reported. Secondly, if the primarysniff does not produce a good match, one or more secondary sniff(s), ifdefined by training, are taken. If a match criterion is not reached, thematching difficulty is noted and the closest match reported. If thegoodness criterion is reached, the match is reported.

[0308] 1) Testing begins with parameters determined by “EstablishPrimary Parameters” section of training.

[0309] 2) Take bleach runs, as described under Training.

[0310] 3) After an inter-run delay, acquire a primary sniff and processthe data.

[0311] 4) The primary sniff data matrix is matched to the primary snifftargets by calculating the SS difference to each target (as describedabove).

[0312] 5) If “goodness” criterion is reached, report the match. Continuetesting.

[0313] 6) Otherwise, does target with lowest SS difference havesecondary sniff(s) defined? If not, note difficulty, report this targetand continue testing.

[0314] 7) Otherwise, set the appropriate secondary parameters.

[0315] 8) Acquire the secondary sniff(s) and process the data.

[0316] 9) The secondary sniff data matrix (or matrices, if more than onesniff) is/are matched to the secondary sniff targets by calculating theSS difference to each target.

[0317] 10) If A “goodness” criterion is reached, report the match.Otherwise, note difficulty, report closest target, and continue testing.

E. Sensitivity Improvements and Other Enhancements

[0318] With certain analytes, for example 2, 4 dinitrotuluene (DNT),which is a major constituent of some explosives, the sensing system ofthe present invention has demonstrated very high sensitivities anddetection limits, for example 2-7 parts per billion (ppb) which are atleast an order of magnitude lower than the best detection limitsreported for conventional fiber optic sensing devices.

[0319] The improved sensitivity, detection and discriminationcapabilities observed with the sensor of the present invention are dueto a number of innovative features. The photodiodes employed in thepresent invention are intrinsically more sensitive than and have largerdynamic range than individual pixels of conventional CCD cameradetectors. The detection surface area of individual sensor photodiodesin the present device is larger than individual pixel areas ofconventional CCD camera detectors. Additionally, due to the surface areaof the LEDs and photodiodes employed in the present invention, largersensor element areas may be employed and sampling is conducted over alarger geometric surface area of individual the sensor elements.Furthermore, the innovative liquid permeable, high porosity high surfacearea sensor substrates of the present invention, further enhance sensorresponse signals due to a substantial increase in sensor surface area tovolume ratios and the volumetric sampling of sensor response signalsgenerated within a three-dimensional substrate-sensor volume.

[0320] Another source of increased sensitivity in the present inventionis the capability to reset the baseline of the amplifiers after turningon the excitation light in order to look only at fluorescencedifferences above background, rather than the background illuminationitself. Thus we are not limited by having to reduce gain or lightintensity to prevent detector saturation as observed with conventionalCCD camera detectors. The amplifiers utilized in the present inventionare specifically designed for resetting signal baseline in order to lookat small fluorescence changes on a large background. In addition,readout from the photodiodes employed in the present invention isintrinsically less. noisy than readout from pixels from CCD cameradetectors employed in conventional devices because the readout speed perchannel with the present invention is lower than that of CCD cameradetectors and higher signal-to-noise ratios are achieved.

[0321] The enhanced sensitivity of the present sensor may be furtheraugmented by utilizing multiple layers of sensing material ‘suspended’in the air stream, employing larger surface area sensor elements andlarger surface area photodiodes, and/or using replicates of multipleidentical detectors in the sensor array from which signals are combinedelectronically. Replicates of different sensing materials may beincorporated into different sensor channels. Using replicates providesadvantages not only with respect to the duplication of data to verifymeasurement reproducibility, but also with regard to reducingnon-correlated noise from electronic components such as amplifiers.

EXAMPLES Example 1 Sensor Response Enhancement

[0322] For evaluating the impact of substrate materials on sensorresponse signal enhancement four different sensor substrates wereevaluated including:

[0323] a) a solid glass coverslip; b) a fine tissue paper (Kimwipe™); c)a porous, low density lens paper; and d) a small ball of cotton. Foursubstrates were employed with sensor elements fabricated from Nile Reddye and polyethylene oxide (PEO) according to the methods describedabove. Two substrates were employed with sensor elements made from apentiptycene-derived phenylenecthynylene polymer 1 (“PDPP1”) synthesizedaccording to the method described previously [SeeYang and Swager inJ.Am.Chem.Soc. 120:11864-25 11873(1998), which is incorporated herein byreference].

[0324] Individual sensor substrate response signals to analyte vaporwere simultaneously measured for each substrate during sample runs. ForPEO-Nile Red sensors, an excitation wavelength of 533 nm, with a 40 nmband pass, and an emission wavelength of 620 nm, with a 10 nm band pass,was used. For the PDPP1 sensor measurements, excitation wavelengths of460 nm and 430 nm, with a 10 nm band pass, and emission wavelengths of488 nm, 500 nm, and 510 nm, with a 10 nm bandpass were employed.

[0325]FIGS. 17a-d shows sensor response signals to saturated methanol,amyl acetate, acetone, and dinitrobenzenene analyte samples for PEO-NileRed dye polymer applied to various substrates. FIG. 18 shows sensorresponse signals to DNT for the PDPP1 polymer applied to two differentsubstrates. FIGS. 19a-b show sensor response signals to variousconcentrations of methanol for PEO-Nile Red dye polymer applied to twodifferent substrates. Each trace represents the analyte response withthe target air response subtracted. Thus, each trace shows only thesignal due to the analyte. Each trace is an average of the signals fromtwo sensors of the same type and from three separate analyte exposures.The traces are not scaled and the y-axis ranges of each plot are thesame.

[0326] After application of fluorescent dye-polymer materials to each ofthe substrates, background fluorescence was measured for each sample toverify that any observed signal enhancement was not due to higherbackground fluorescence. The same excitation and emission wavelengthsused in the response signal measurements shown in FIGS. 17a-b, 18, and19 a-b were used for background fluorescence measurements. Voltagemeasurements were taken from the output of the amplifiers at a testpoint between the voltage divider and the A/D converters. For backgroundfluorescence measurements, LED intensity was adjusted to a sufficientlylow level such that none of the sensors saturated the amplifier. Thisintensity was much lower than that used during the analyte measurementsshown in the plots. For background measurements, the voltages wererecorded on a storage oscilloscope while the LEDs were switched on.These measurements represent the difference between the amplifier outputbefore and immediately after the LEDs were turned on before anysignificant photo-bleaching occurred. Raw output from detectoramplifiers was measured in volts. Background fluorescence for eachsubstrate sample were measured as follows:

[0327] Glass—0.325

[0328] Kimwipe™—0.25

[0329] Lens paper—0.275

[0330] Cotton—1.2

[0331]FIGS. 17a-d shows that both Kimwipe™ and cotton sensor substratesproduced substantially enhanced response signals compared toconventional glass substrates. While the background fluorescencemeasurements indicate that cotton substrates produces the highestbackground fluorescence, as shown in FIGS. 17a-d, cotton substratesensor response signals were comparable to Kimwipe™ substrates formethanol analyte and produced the most enhanced response signals withamyl acetate and dinitrobenzene analytes. FIG. 18 shows a dramaticsignal enhancement for saturated DNT analyte produced with PDPP1 polymerapplied to a Kimwipe™ substrate when compared to glass coverslips.Comparison of the response signals produced by PEO-Nile Red dye polymeron glass and Kimwipe™ substrates are shown for various concentrations ofmethanol analyte samples in FIGS. 19a and 19 b. While no enhancement wasobserved at dilute concentrations of methanol, a substantial signalenhancement was observed at higher concentrations of methanol analyteusing the innovative substrates of the present invention.

Example 2 Analyte Response Characteristics

[0332] As a demonstration of the analyte detection capability of thesensor of the present invention, eight test samples were prepared fromanalyte-saturated air. The target analytes comprised an air baselinesample, acetone, amyl acetate, carvone, chloroform, cloves, a commericalcologne (Drakkor Noir™), and isopropanol.

[0333] For the experiment, a nine element sensor array was utilized. Themethods used for fabrication the sensor elements of the array aredescribed above and in a previous publication [see J. White, et al.,Anal.Chem. 68(13):2191-2202(1996)]. The sensor element materialsemployed in this sensor array are as follows: 0 PABS 1 PDPO/Alumina 2 EC3 Dow 4 PBA 5 PC/Alumina 6 Dow/Alumina 7 PSAN 8 PC

[0334] Each analyte sample was sampled for 1 second and data was takenover a 2.5 sec data acquisition time with data time points taken every250 ms. For each analyte, ten samples were measured over a 2.4 secondperiod. For these experiments, all sensors were illuminated at anexcitation wavelength of 530 nm (40 nm bandpass) and sensor responseswere monitored at an emission wavelength of 620 nm (20 nm bandpass) byapplication of excitation filters to the LEDs and emission filters tophotodiode detectors.

[0335]FIG. 20 shows typical spatio-temporal response patterns of asensor array of the present invention to eight different analytesamples. Each z-axis value in the matrix represents the magnitude offluorescence above or below the baseline at a specific time point foreach specific sensor element. The results shown in FIG. 20 clearlydemonstrate the ability of the semi-selective, cross-reactive sensorarray of the present invention to detect and discriminate among a widediversity of analytes.

Example 3 Smart Mode Test Results

[0336] To demonstrate one embodiment of the innovative smart modesampling, detection, discrimination, and identification capability ofthe present invention, the number of samples taken (“sniffs”) andsampling times (“sniff duration”) were adjusted and controlledon-the-fly using real-time feedback obtained from prior samplingresults.

[0337] Since it is generally desirable to provide for sampling at highfrequencies and short durations, the sensing device of the presentinvention provides for frequent and rapid environmental sensing. Twolimiting characteristics of dye sensors affect how frequent and how fastsamples can be taken. First, fluorescent sensors tend to bleach withlong exposure to the excitation light, thereby losing their sensitivityto analytes. Secondly, sensors tend to yield smaller response signalsupon long and frequent exposure to analyte and some relaxation orrecovery time is generally necessary after such exposure.

[0338] Typically, for frequent sampling, it is preferable to make theanalyte and light exposures brief. However, brief exposures tend toproduce smaller response signals and thus compromise sensor detectionlimits. These limitations are overcome by smart mode sampling wherereal-time sampling feedback is applied to optimize sampling time and thenumber of samples taken. In this mode, short samples are acquired first,results are checked against a defined statistical criteria to determinesample validity, and longer samples are subsequently acquired only wherethe results of short sampling are ambiguous or unreliable.

[0339] To demonstrate this particular implementation of the smart modesampling capability of the present invention, an eight sensor arraycomprising two replicates of four dye-polymer sensors were employed fordiscriminating acetone from air. The sensors used for smart mode sensingare listed below together with their emission and excitationwavelengths. The cellulose fiber substrate used for sensors 1-3 wascommercial tissue paper sold as Kimwipe™. The glass fiber substrate usedfor sensor 4 was a commercial filter paper sold as MilliPore™ Type APFAglass fiber filter (1.6 um retention/500-500 um thick). These sensorswere fabricated according to the methods described above. #1. Nile Red /Poly(N-vinylpyrrolidone on [ex. 533 nm / em. 600 nm] cellulose fibersubstrate #2. Nile Red / Poly(ethylcellulose) [ex. 533 nm / em. 610] oncellulose fiber substrate #3. Nile Red / Poly (dimethylsiloxane) [ex.533 nm / em. 633] on cellulose fiber substrate #4. Nile Red on a glassfiber substrate [ex. 533 nm / em. 650].

[0340] Prior to actual analyte sampling, the sensor was trained for thetarget analytes according to the methods described previously above.FIG. 21 provides a schematic flowchart of the specific training stepsemployed in this experiment. Preliminary target data were acquired foreach sensor in the array by sampling air and acetone-saturated air forshort and long sampling (“sniff”) times.

[0341] The target sampling results for each analyte and each sensor areprovided in FIGS. 23a-d, where responses to both air and acetone areshown for each sensor for both short and long sample times (sniffs). Foreach analyte, five data points were acquired at 100 ms intervals.Sampling duration was 100 ms for short sniffs and 200 ms for longsniffs. The long sniffs were acquired immediately after the short sniff.It is worth noting that the amplitude of the second sniff response willrecover if a long time interval occurs between sniffs. The traces shownin the graphs are the average of two sensor responses for four differentruns.

[0342] The target data in FIGS. 23a-d are plotted to clarify thetemporal relationship between short and long sniffs in the trainingmode. The horizontal bars toward the bottom of each graph indicate theduration of the two sniffs with the short sniff being first, followedabout two seconds later by the long sniff. The dotted lines in thefigure depict a two second break in the time axis between sniffs. Thetwo second delay is the amount of time it takes for the embeddedcomputer to process the data from the first sniff and to start up thesecond sniff. The duration of this delay will vary with the specifichardware configuration employed. This interval may be reduced by eitherconverting most of the data calculations from floating point to integerarithmetic or using a faster computer. Computational power is not alimiting factor. Note that the response intensity range of the y-axisare the same for each figure. The data shown in FIGS. 23a-d are scaledthe same way that the embedded computer scales the data during itsprocessing. The most significant features of these plots are therelative signal amplitudes for each analyte and the contribution of eachresponse signal to analyte discrimination.

[0343] As shown in FIGS. 23a-d, sensor #1 (FIG. 23a) demonstrated poordiscrimination for acetone with short sniff sampling whereas sensor #2(FIG. 23b), sensor #3 (FIG. 23c), and sensor #4 (FIG. 23d) showmarginally better discrimination with short sniffs. With longer sniffsampling, sensor #1 shows improved discrimination, sensor #3 showsmarginally similar discrimination and sensors #2 and #4 showdramatically improved discrimination for acetone. In an ideal samplingapplication, where sensor element response signals are large andnoise-free, the sampling system would normally identify target analyteswithout difficulty. In this example, the less responsive sensors #1 and#3 were chosen to replicate, in a controlled manner, a real samplingsituation where the sensing device may become confused due toinconsistent or conflicting response data obtained from multiple sensorsand would make errors in identification. For these realistic scenarios,the smart mode sampling would be most useful for detecting,discriminating, and identifying analytes where response signals areeither small and/or noisy.

[0344]FIG. 22 provides a schematic flowchart of the sampling proceduresused for smart mode sampling in this experiment. Initially, short sniffswere acquired every 10 seconds. The measured response was compared tothe short sniff targets for air and acetone using a sum-of-squaresmatching algorithm that is described above. Normally, the target withthe smaller match score, or lower sum of least squares, would bereported as the identity of the test analyte. In the smart samplingmode, all target match scores, in this case acetone and air, wereevaluated to determine how ‘good’ the match is. If the match was not‘good’ enough, a second, longer sniff was acquired and that match wasreported. For detecting target analytes, a ‘goodness’ criterion wasapplied to the ratio of the match scores for each analyte. The largermatch score may be evaluated by a criterion wherein it must be somethreshold number of times greater than the smaller match score. Twoexamples of this evaluation method is provided below which demonstratethe improvement in acetone recognition using smart mode sensing.Following the approach used in signal detection theory, test matricesare provided in a simplified format which represents the numbers ofhits, misses, false alarms (FA), and correct rejections (CR):

[0345] In each example, fifty sample runs were made, with 25 runs eachof air and acetone. Samples were collected in alternating blocks offive, five air, then five acetone, then five air, etc. For a directcomparison, all data were collected in ‘smart nose’ mode. For thestandard mode representation, only the first short sniff was considered.For the smart mode representation, the final outcome (whether or not oneor two sniffs were acquired) was considered.

[0346] Example #1:

[0347] a) Standard mode

[0348] b) Smart nose mode

[0349] In this example, the ‘goodness’ criterion was set to two (i.e.the ratio of the larger match score to the smaller match score had to begreater than two). In both modes, the number of correct rejections(reporting air when air was presented) was high. The smart sampling modeimproved the number of hits (from 48% to 76%). The smart mode evaluationrequired 18 additional long sniffs for this improvement.

[0350] Example #2:

[0351] a) Standard Mode

[0352] b) Smart nose mode

[0353] In this second example, the ‘goodness’ criterion was set tothree. Again, the number of correct rejections was high for both modes.The more stringent ‘goodness’ criterion improved the number of hits to92%, requiring 25 additional long sniffs.

Example 4

[0354] In order to demonstrate the unique sensitivity, detection, anddiscrimination capabilities of the sensor of the present invention, fivevapor mixtures of analyte-saturated air were sampled with a nine elementsensor array of the present invention and a sixteen element fiber opticsensor array for comparing the relative sensitivity and discriminatingcapability of the two sensing devices. Table 4.1 lists the sensorelement types employed for each sensor array in the comparative testing.These sensors were fabricated according to the methods described above.The fabrication methods employed for the sensor elements and fiber opticsensor device are described previously [see J. White, et al., Anal.Chem. 68(1 3):2191 -2202(1996)].

[0355] The response of the fiber optic sensing device to air, methanol,amyl acetate, acetyl acetate, and xylene analytes was initiallyevaluated using a CCD camera detection system and an enclosed, positivepressure, sample delivery method described previously (see J. White, etal., Anal. Chem. 68:2191-2202 (1996)). During sampling, the CCD gain wasadjusted such that non-saturating signals were obtained from all sensorsin the fiber optic array. The maximum gain which would providedetectable responses from less responsive sensors and not saturate theCCD amplifier with highly response sensors was utilized. Unlike thepresent invention, the fiber optic sensor employs a CCD camera detectorthat does not provide for adjusting the gain for each sensor elementbased on the sensor element response signal. This is an undesirablelimitation in individual sensor response capabilities since the responsesignal for each sensor element in the array can not be optimized withthis device. In contrast, the present sensing device has the capabilityfor adjusting the gain of individual sensor channels to obtain maximumresponse signal from each sensor in the array. Such a capability isparticularly advantageous when there is a significant difference in theresponse signals of sensor array elements to specific analytes. Byproviding for gain adjustment of individual sensor channels, optimumdetection, discrimination, and sensor response utilization is achievedby optimizing signal response intensity and signal to noise ratios foreach sensor element in the array. This capability for individuallyadjusting sensor element response signal is essentially impossible toachieve with the conventional CCD camera detectors that are typicallyemployed with fiber optic sensors. TABLE 4.1 Sensor Elements Employedfor Comparative Performance Testing Element No. Present InventionElement No. Fiber Optic Sensor 7 Dow/alumina 2 background - no polymer 4Dow 3 PS802/20% MMA 1 PABS 4 cellulose/alumina/ cellulose 8 PSAN 5RMS-044/ 20% MMA 5 PBA 6 (inoperative) 2 PDPO/alumina 7 Dow/alumina 9 PC8 Dow/alumina/ PDPO 6 PC/alumina 9 P5802/PS901.5 3 EC 10 P5802/10% MMA11 PDPO 12 Dow (2 dips) 13 RMS-044 14 PS901.5 15 PS802 16Dow/alumina/Dow 17 Dow(Sdips) 18 (inoperative) 19 PC/PSAN/alumina 20(inoperative) 21 cellulose/PDPO and beads

[0356] While initial sampling tests with the fiber optic sensor employedan enclosed, positive pressure chamber that contained analyte vapors, inorder to make a direct comparison of the sensing performance of the twosensing devices, a small port hole was drilled into the sample chamberarea of the present invention for positioning the fiber optic sensor.With this configuration, response measurements for both sensing devicescould be directly compared using the same analyte sampling pulsegenerated by the sampling valves and fans of the present invention.

[0357] Data were acquired from both the fiber optic sensor and thepresent sensor while introducing odors to the sample chamber via thevalve and fan assembly of the present invention. In this manner, thedifference in sensitivity between the two sensors to pulses of analytegenerated by the same odor delivery method could be monitored. To avoidinterference during data acquisition for each sensing device, the fiberoptic sensor excitation light source was turned off when acquiring datafrom the present sensor and the LED excitation light sources were turnedoff when acquiring data from the fiber optic sensor . Both sensingdevices employed the same sensor excitation wavelength of 530 nm (40 nmbandpass) and same sensor emission wavelength of 620 nm (20 nm bandpass)by applying excitation filters to the light source and emission filtersto the detection means for each sensing device.

[0358] In comparing the fiber optic sensor response to methanol duringinitial testing, the amplitude of the fiber optic signal obtained withinthe sample chamber was generally about half the amplitude of the signalobtained using an enclosed, positive pressure sampling container whichis typically used when making sample measurements with this device.While reduced response signal could be overcome by increasing detectorgain settings, this was not possible with the fiber optic sensor sincethe CCD amplifier was set at the maximum permissible gain which wouldavoid CCD detector saturation from the high fluorescence background ofthe sensor elements. In contrast, the sensor of the present inventionproduced a much larger response signal to the same methanol analytepulse. Although very large response signals may saturate the amplifierof the present sensor, it is still possible to use the full range of theA/D conversion for all the sensors in the present array since thebaseline intensities for every sensors may be reset to a common value.

[0359] For the plots shown in FIGS. 24a-b, 24 d, 25 a-b, and 26 a-c afull-scale y-axis plotting range of 4000 response intensity units wasused for displaying the signal response for as a function of time forboth sensing devices. This scale approximated the resolution limit forsensor response measurements since all data were digitized to 12 bitswhich resulted in response data values ranging from 0 to 4096 for bothdevices. For the fiber optic sensor, data are plotted as pixel valuesand for the present sensor, data are plotted as fluorescenceanalog/digital values. For the plots shown in FIGS. 24c, 24 e, and 25c-d, due to the low response signals produced by the fiber opticsensors, a much smaller range is plotted which shows much lower signalchanges than the data obtained with the present invention plotted atfull scale in FIGS. 26a-c. Due to the typically slower sensor responsetimes observed with the fiber optic sensor, measurements were made overa 20 second time frame for this device whereas a 5 second measurementperiod was used for the present invention. In comparing sensingperformance of the two sensor devices, the most important parameter isthe relative amplitude of the signals obtained for individual sensorelements in response to analytes.

[0360] Since, as discussed above, the baseline signal for individualfiber optic sensor elements could not be reset to avoid saturation, thevideo gain for the fiber optic sensor measurements was set at themaximum gain that prevented the brightest sensors from saturating theCCD. This led to a compromise in response signal response for sensors inthe fiber optic array since signal gain for individual sensors could notbe adjusted for maximum sensitivity and resolution. Thus, responsesignals from sensors producing low signal could not be amplified withoutsaturating high signal producing sensors and response signals fromsensors producing high signal could not be reduced without risking lossof signal from less responsive sensors. In contrast, since the sensor ofthe present invention has the capability to both reset responsebaselines for all sensors in the array and then maximize sensor gain forall sensors, the sensor of the present invention provided much higherresponse signal, resolution and sensitivity for optimum sensor responseto analytes.

[0361] In FIGS. 24a-e, the sensor responses for two sensor elements ofthe fiber optic sensor, a cellulose-alumina sensor and a Dow sensor, areshown for a methanol-saturated analyte sample and a 1:10 dilution ofthis analyte sample. The compositions and methods for fabricating thesesensors are described above. The cellulose-alumina sensor datarepresents the most responsive (i.e. bright) sensor observed formethanol with the fiber optic devices while the Dow sensor datarepresents a typical, moderately responsive (i.e. less bright) sensor.In FIG. 24a, the upper pixel intensity trace is from the bright sensorand the lower trace from the less bright sensor. This plot shows asubstantial difference in intensity for the two sensors such that thegain of the Dow sensor cannot be increased without saturating thecellulose-alumina sensor, resulting in the loss of sensor reliability.The full-scale plot of FIG. 24b shows the minimal change in pixelintensity of the less bright Dow sensor upon exposure to methanol aseither a saturated analyte sample or a 1:10 sample dilution. These dataare replotted in FIG. 24c on a much finer scale and clearly shows therelatively low response signal of this sensor to methanol where asaturated analyte sample produces only about 40 pixel intensity unitchange, or 1% of full-scale, while a dilute analyte sample produces onlyabout a 15 unit change, or about 0.4% of full-scale. The full-scale plotof FIG. 24d shows the relatively modest change in pixel intensity of thebright cellulose-alumina sensor upon exposure to saturated methanolanalyte solution and a diluted sample solution. These data are replottedin FIG. 24e on a finer scale and show a modest 200 unit increase inintensity, or 5% of full-scale, for the saturated analyte, and less thana 50 unit change, or about 1 % change of full-scale, for the diluteanalyte sample. In dramatic contrast to the fiber optic sensor responsemeasurements, the increased sensitivity, resolution, and detectioncapability of the innovative sensor of the present invention tosaturated methanol and dilute methanol analyte samples is shown in FIG.26a where data for the less bright Dow sensor material are provided.With the present sensor, the dilute analyte exhibits about a 1100 unitchange in intensity, or 25% of full-scale whereas the saturated analyteshows over a 1700 unit change in intensity, or about 43% of full-scale.With the fiber optic device, the, equivalent sensor material producedonly from 1 to 10% of the signal of the present invention in response tothe same analyte solutions.

[0362] Similar results were observed with other analyte samples. FIGS.25a-b show the minimal pixel intensity change of the fiber optic deviceto saturated and diluted amyl acetate analyte solutions where a changeof only 27 to 38 intensity units was observed with the Dow sensorelement. In contrast, FIG. 26b shows the significant intensity change ofthe present sensor device to saturated and diluted amyl acetate samplesolutions where a change of 500 to 1000 intensity units was observedwith the Dow sensor element. The fiber optic device apparently producedonly 3-5% of the signal of the present invention in response to the sameanalyte solutions. FIGS. 25c-d show that the fiber optic device has anextremely low responsivity to saturated and diluted xylene analytesolutions where the response signal is relatively noisy and a change ofonly about three intensity units is observed for each analyte sample. Incontrast, FIG. 26c shows the significant intensity change of the presentsensor device to saturated and diluted xylene sample solutions where achange of about 50-250 intensity units was observed with the Dow sensorelement in response to the dilute and concentrated analytes. The fiberoptic device apparently produced only 1-4% of the signal of the presentinvention in response to the same analyte solutions.

[0363] These results demonstrate that the response signal amplitude,resolution, sensitivity, detection and discrimination capability thatcan be achieved with the innovative sensor of the present invention issubstantially better than even the largest signal obtained from the mostresponsive sensor materials with fiber optic sensor devices. These dataunambiguously demonstrate the enhanced detection and discriminationcapability of the sensor of the present invention which provides forhigh signal to noise, increased sensitivity, lower detection andidentification limits and greater discrimination in analyte sensing. Inaddition, from these results, it appears that the response time of theinnovative sensor of the present invention is significantly faster thanfiber optic sensor devices.

[0364] The ability to reset the amplifier in the device of the presentinvention provides the capability to sense from all sensors in the arraysimultaneously without compromising signal information from either themost responsive or least responsive elements in the array. Furthermore,this innovative feature of the sensor of the present inventions enablesuse of higher gain settings and reduced noise, resulting in largerresponse signals and improved analyte detection and discriminationcapability. These response measurement results clearly demonstrate theunique and advantageous sensitivity, detection limits, anddiscrimination capabilities of the device of the present invention whencompared to conventional sensor designs under the same test conditions.

[0365] Having described the preferred embodiments of the invention, itwill now become apparent to one of skill in the art that otherembodiments incorporating the concepts may be

What is claimed is:
 1. An optical sensor for detecting target analytesin a fluid, said sensor comprising: a fluid-permeable, textured dyesubstrate having a high surface area and high surface area to volumeratio, said substrate having high open porosity, said substrate havinghigh permeability to fluids; and a dye compound dispersed on a pluralityof internal and external surfaces within said textured dye substrate,said dye compound providing a characteristic optical response whensubjected to excitation light energy in the presence of said targetanalytes.
 2. The sensor of claim 1 wherein said dye substrate iscomprised of a fibrous material.
 3. The sensor of claim 2 wherein saidfibrous material is selected from the group consisting of papers,tissues, textiles, woven fabrics, felts, fibers, fiber bundles,composites, and laminates of the same.
 4. The sensor of claim 1 whereinsaid dye substrate is comprised of a particulate material.
 5. The sensorof claim 4 wherein said particulate is selected from the groupconsisting of glasses, silicas, aluminas, ceramics, polymers, plastics,metals composites, sintered powders, and fritted assemblages of thesame.
 6. The sensor of claim 1 wherein said dye compound comprises afluorescent dye.
 7. The sensor of claim 6 wherein said dye compoundfurther comprises a polymer.
 8. The sensor of claim 6 wherein said dyefluorescent dye is a solvatochromic dye.
 9. The sensor of claim 8wherein said solvatochromic dye is selected from the group consisting ofNile Red, Prodan, 6-propionyl-2-(N,N-dimethylamino) napthalene,Acrylodan, and 6-acryloyl(dimethylamino) napthalene.
 10. A sensor arrayfor detecting target analytes in a fluid, said sensor array comprising:a plurality of fluid-permeable, textured dye substrates having a highsurface area and high surface area to volume ratio, said substrateshaving high open porosity, said substrates having high permeability tofluids; a plurality of dye compounds dispersed on a plurality ofinternal and external surfaces within said textured dye substrates, saiddye compounds providing a characteristic optical response when subjectedto excitation light energy in the presence of a target analyte; said dyesubstrates and said dye compounds forming a plurality of sensor arrayelements; and a substrate support.
 11. The sensor array of claim 10wherein said dye substrates are comprised of a fibrous material.
 12. Thesensor of claim 11 wherein said fibrous material is selected from thegroup consisting of papers, tissues, textiles, woven fabrics, felts,fibers, fiber bundles, composites, and laminates of the same.
 13. Thesensor of claim 10 wherein said dye substrates are comprised of aparticulate material.
 14. The sensor of claim 13 wherein saidparticulate is selected from the group consisting of glasses, silicas,aluminas, ceramics, polymers, plastics, metals composites, sinteredpowders, and fritted assemblages of the same.
 15. The sensor of claim 10wherein said dye compounds comprise a fluorescent dye.
 16. The sensor ofclaim 15 wherein said dye compounds further comprise a polymer.
 17. Thesensor of claim 15 wherein said fluorescent dye is a solvatochromic dye.selected from the group consisting of Nile Red, Prodan,6-propionyl-2-(N,N-dimethylamino)napthalene, Acrylodan, and6-acryloyl(dimethylamino) napthalene.
 18. A sensor array according toclaim 10 further comprising an excitation light energy source in opticalcommunication with said sensor array elements.
 19. A sensor arrayaccording to claim 11 further comprising an emission light energydetection means in optical communication with said sensor arrayelements.
 20. A method for detecting a target analyte in a fluidcomprising the steps of: a) contacting said sample with a sensor arraycomprising: i) a fluid-permeable, textured dye substrate having a highsurface area and high. surface area to volume ratio, said substratehaving high open porosity, said substrate having high permeability tofluids; and ii) a dye compound dispersed on a plurality of internal andexternal surfaces within said textured dye substrate, said dye compoundproviding a characteristic optical response when subjected to excitationlight energy in the presence of a target analyte; and b) detecting thepresence or absence of said target analyte.
 21. The method of claim 20wherein said contacting further comprises drawing said fluid into asample chamber and exposing said array to said fluid for no more thanfive seconds.
 22. The method of claim 20 wherein said detecting furthercomprises: illuminating said sensor with excitation light energy; andmeasuring an optical response produced by said sensor due to thepresence of said analyte with a detector means.
 23. The method of claim22 further comprising identifying said analyte by employing apattern-matching algorithm; and comparing said optical response of saidsensor with said characteristic optical response.
 24. The method ofclaim 22 further comprising identifying said analyte by providingspatio-temporal response patterns of said optical response; andrecognizing said patterns through a method selected from the groupconsisting of a template matching, neural networks, delay line neuralnetworks, or statistical analysis.
 25. A method for detecting a targetanalyte in a fluid comprising the steps of: setting primary samplingparameters for a sensor array; contacting said fluid with said array;detecting a first plurality of optical responses produced by interactionof said fluid with said array; comparing said first plurality ofresponses to a first stored spatio-temporal response for said primaryparameters for said analyte; setting secondary sampling parameters forsaid array wherein at least one sampling parameter is changed; detectinga second plurality of optical responses produced by interaction of saidfluid with said array; comparing said second plurality of responses to asecond stored spatio-temporal response for said secondary parameters forsaid analyte; and detecting the presence or absence of said analyte. 26.The method of claim 25 wherein said setting primary sampling parameterscomprises: adjusting an excitation light source to a non-zero minimumintensity; setting a fluid sampling time to a non-zero minimum time;adjusting said fluid flow to a non-zero minimum flow rate; and setting anumber of sampling time points to a non-zero minimum. setting a numberof sniff samples to a maximum
 27. The method of claim 25 wherein saidsetting secondary sampling parameters comprises: incrementing saidnumber of sniff samples by at least one; selecting said at least oneparameter setting from the group consisting of amplifier gain, fluidsampling time, fluid flow rate, number of sampling time points, samplesniff rate, amplifier high pass filtering, excitation light sourceintensity, and exhale velocity; and modifying said at least oneparameter setting from an initial setting value.
 28. A sensing systemfor detecting and identifying an analyte in a fluid comprising: across-reactive sensor array comprising a plurality of dye compounds, aplurality of porous, permeable, high surface area, textured dyesubstrates, said dye compounds and said dye substrates forming aplurality of sensor elements, a substrate support; an excitation lightsource array comprising a plurality of light sources optically coupledto said sensor elements; a detector array comprising a plurality ofdetectors optically coupled to said sensor elements; a sample chamberfor housing said sensor elements, said light source array, said detectorarray; a sampling means enclosed in said chamber for drawing said fluidinto said chamber for contact with said sensor array for a controlledexposure time; a controller means in electrical communication with saidlight sources, said detectors, and said sampling means, said controllermeans electrically coordinating and switching said sampling means withsaid light sources and said detectors for sampling said fluid, measuringoptical responses of said array sensors to said fluid, and detectingsaid analyte; and an analyte identification algorithm for comparing saidmeasured sensor optical responses to characteristic optical responses ofsaid sensors to target analytes and identifying said analyte in saidfluid.
 29. A smart sensing system for intelligent detecting andidentifying an analyte in a fluid comprising: a cross-reactive sensorarray comprising a plurality of sensors; a detector array comprising aplurality of detectors in communication with said sensors; a samplingchamber for housing said sensor array and said detector array; asampling means enclosed in said chamber for drawing said fluid into saidchamber for contact with said sensor array for a controlled exposuretime; a microcontroller in electrical communication with said samplingmeans and said detector array, said controller means electricallycoordinating and switching said sampling means and said detector arrayfor sampling said fluid, measuring responses of said sensors to saidfluid, detecting said analyte, and reporting an analyte detectionresult; an intelligent sampling algorithm for directing saidmicrocontroller, said sampling algorithm selecting sensors anddetectors, said sampling algorithm coordinating said electricalcommunication for said switching, said sampling, said measuring, saiddetecting and said reporting, said sampling algorithm setting first andsecond sampling parameters; and an analyte identification algorithm incommunication with said sampling algorithm and said microcontroller,said identification algorithm comparing said measured sensor opticalresponses to characteristic responses of said sensors to target analytesand identifying said analyte in said fluid.
 30. The sensing system ofclaim 29 wherein said identification algorithm comprises a responsereport comparing a spatio-temporal pattern of said measured opticalresponses to a spatio-temporal pattern of said characteristic responses;and an identification report selected from the group consisting of apattern match, a delay line neural network match, and a neuronal networkmatch.